Resistor element, stress sensor and method for manufacturing them Number:7,151,431 from the United States Patent and Trademark Office (PTO) owispatent

Title: Resistor element, stress sensor and method for manufacturing them

Abstract: A stress sensor in which the direction and magnitude of a stress being applied to a post (6) bonded to or integrated with the surface of an insulating board (3) can be grasped from variation in the resistance of a plurality of resistor elements (8) being stimulated by application of the stress while suppressing variation in the shape of each resistor (2). The resistor element (8) comprises a resistor (4) formed, by screen print, between a pair of electrodes for the resistor element, i.e. circuit pattern electrodes (1), arranged on the surface of the insulating board (3). The electrode is connected, through a conductor (9), with a board terminal part (5) arranged at one end of the insulating board (3). The electrode (1) and the conductor (9) or a print accuracy adjusting member (7) have a constant height from the surface of the insulating board (3). Arrangement of the conductor (9), the electrode (1) and the print accuracy adjusting member (7) is entirely identical or similar for the plurality of resistor elements (8) in the vicinity thereof.

Patent Number: 7,151,431 Issued on 12/19/2006 to Ooba,   et al.

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Inventors:	Ooba; Etsuo (Nagano, JP), Inukai; Atsuomi (Nagano, JP), Karasawa; Fumiaki (Nagano, JP), Yajima; Hiroshi (Nagano, JP)
Assignee:	Elantech Devices Corporation (TW)
Appl. No.:	10/467,144
Filed:	February 14, 2002
PCT Filed:	February 14, 2002
PCT No.:	PCT/JP02/01250
371(c)(1),(2),(4) Date:	August 05, 2003
PCT Pub. No.:	WO02/065487
PCT Pub. Date:	August 22, 2002

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Foreign Application Priority Data

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Feb 16, 2001 [JP]			2001-039875
Feb 22, 2001 [JP]			2001-046909
Feb 22, 2001 [JP]			2001-046910
Jul 31, 2001 [JP]			2001-230861

Current U.S. Class:	338/2 ; 338/47; 73/720
Current International Class:	G01L 1/22 (20060101)
Field of Search:	338/2-6,39,42,47 73/720,746,862.474

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References Cited [Referenced By]

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U.S. Patent Documents

	3341794		September 1967		Stedman
	4104421		August 1978		Maher et al.
	4481497		November 1984		Kurtz et al.
	4488436		December 1984		Mohri et al.
	4506250		March 1985		Kirby
	4540463		September 1985		Kakuhashi et al.
	4771261		September 1988		Benini
	4966039		October 1990		Dell'Acqua
	4974596		December 1990		Frank
	5209122		May 1993		Matly et al.
	5317920		June 1994		Kremidas
	6439056		August 2002		Jonsson
	2001/0015720		August 2001		Inukai

Foreign Patent Documents

	08-308204		Nov., 1996		JP
	10-148590		Jun., 1998		JP

Other References

Preliminary examination report from corresponding PCT/JP02/01250. cited by other . International Search Report--PCT/JP02/01250; ISA/JPO, completed May 9, 2002. cited by other . Patent Abstracts of Japan for JP2000-267803. cited by other.

Primary Examiner: Hoang; Tu
Attorney, Agent or Firm: Harness, Dickey & Pierce, P.L.C.

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Claims

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The invention claimed is:

1. A stress sensor comprising: a insulating board having first and second surfaces, the second surface being opposite the first surface; a post bonded to or integrated with the first surface of the insulating board; a plurality of resistor elements disposed on the second surface of the insulating board, the resistor elements being composed of a plurality of resistors; a plurality of resistor-element electrodes disposed on the second surface of the insulating board; a plurality of board terminal pads disposed on the second surface of the insulating board proximate one end thereof; and a plurality of conductors disposed on the second surface of the insulating board, wherein the resistors are formed by a screen printing method between pairs of the resistor-element electrodes, the resistor-element electrodes are connected to the board terminal pads through the conductors, and the resistor-element electrodes and the conductors have a predetermined height from the second surface of the insulating board, the arrangements of the conductors and the resistor-element electrodes, in the vicinities of the respective resistor elements, are equal or similar to each other, and the direction and magnitude of a stress applied to the post are grasped from variation in resistance of the resistor elements caused by stimulation resulting from the application of the stress while suppressing variation in shape of each resistor element.

2. The stress sensor of claim 1, wherein said electrodes composed of parts of said conductors, obtained by an additive method; and said resistor elements formed by film formation, wherein the ratio L/h of the distance (L) between said pair of the electrodes to the height (h) of the electrodes is 30 or more.

3. The stress sensor of claim 1, wherein said electrodes composed of parts of said conductors, obtained by an additive method; and said resistor elements formed by film formation, wherein a height deviation of said pair of the electrodes is 0 or less.

4. The stress sensor of claim 1, wherein the arrangements of the conductors and the resistor-element electrodes, in the vicinities of the respective resistor elements, are each formed so as to surround at least three sides of each of the resistors.

5. The stress sensor of claim 1, wherein the resistor-element electrodes and the conductors are disposed so as to intermittently surround each of the resistor elements.

6. The stress sensor of claim 1, wherein the resistor-element electrodes and the conductors are disposed so as to continuously surround each of the resistor elements.

7. The stress sensor of claim 1, further comprising print accuracy adjustment members having the predetermined height from the second surface of the insulating board.

8. The stress sensor of claim 7, wherein the arrangements of the conductors, the resistor-element electrodes, and the print accuracy adjustment members, in the vicinities of the respective resistor elements, are equal or similar to each other.

9. The stress sensor of claim 7, wherein the arrangements of the conductors, the resistor-element electrodes, and the print accuracy adjustment members, in the vicinities of the respective resistor elements, are each formed so as to surround at least three sides of each of the resistors.

10. The stress sensor of claim 7, wherein the resistor-element electrodes, the conductors, and the print accuracy adjustment members are disposed so as to intermittently surround each of the resistor elements.

11. The stress sensor of claim 7, wherein the resistor-element electrodes, the conductors, and the print accuracy adjustment members are disposed so as to continuously surround each of the resistor elements.

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Description

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TECHNICAL FIELD

The present invention relates to resistor elements and stress sensors as one application filed thereof, which can be used, for example, for a pointing device for personal computers or a multifunctional and multidirectional switch for various electronic devices.

BACKGROUND ART

A stress sensor has been disclosed in Japanese Unexamined Patent Application Publication No. 2000-267803, which is capable of grasping the direction and magnitude of a stress applied to a post bonded to or integrated with a surface of an insulating board from variation in resistance of a plurality of resistor elements caused by stimulation provided thereto resulting form the application of the stress to the post. The formation of the resistor elements thus disclosed, which elements form a strain gage, is performed by screen printing of all constituent elements of the resistor elements on a surface of a ceramic board.

The structure is formed as shown in FIG. 15, in which four resistor elements 22 are disposed on two lines, which are along a surface of an insulating board 20 and perpendicularly intersect each other at the center of a surface the insulating board 20, and are provided at substantially the same distance from the intersecting point. In addition, in the structure described above, a post 30 having a square bottom surface is bonded so that the center thereof coincides with the center of the surface of the insulating board 20 and that individual sides of the bottom surface of the post 30 oppose the respective resistor elements 22. In addition, board terminal parts 24 are provided at end portions along the entire periphery of the insulating board 20 at approximately regular intervals. Since conductors (electrodes) to be connected to the resistor elements 22 and the board terminal parts 24 are formed on the surface of the insulating board 20 by a screen printing method, they have a uniform (predetermined) height from the surface of the insulating board 20.

In recent years, in addition to stress sensors having the structure in which all constituents for constituting resistor elements are formed by screen printing on a surface of a ceramic board, development of stress sensors using an insulating board provided with conductors, which are obtained by partly removing a conductor layer on a surface as remains, has also been carried out. The reasons for this is that, compared to thick film techniques such as a screen printing technique, the conductors of the insulating board described above can be easily processed to have fine patterns, and in addition, an advantage of low manufacturing cost can also be obtained.

However, when the insulating board for a stress sensor is an insulating board having conductors which are obtained by partly removing a conductive layer on a surface as remains, and when the stress sensor uses parts of the conductors 9 as electrodes and resistor elements as a strain gage, each element formed of a resistor provided between a respective pair of the electrodes on the surface of the insulating board, a problem different from that of the conventional technique described above may arise.

In the past, the electrodes (conductors) constituting the resistor elements were formed by a screen printing method, and in the above technique, the conductors are formed of the remains obtained by partly removing the conductor layer on the surface; hence, the problem is generated by the difference described above.

The difference described above is schematically shown in FIG. 7. FIG. 7(a) is a schematic cross-sectional view of a resistor element 8 using conductors (circuit pattern electrodes 1) as electrodes, which are obtained by partly removing a conductor layer on a surface of an insulating board 3. FIG. 7(b) is a schematic cross-sectional view of a resistor element 8 using conductors (resistor-element electrodes (hereinafter referred to as "thick electrodes)) obtained by screen printing, which is one of thick film techniques.

The conductor height shown in FIG. 7(a) mostly depends on the thickness of the conductor layer which is originally disposed on a surface of the insulating board 3 and is formed of copper or the like. In general, this thickness is approximately from 18 to 36 .mu.m. In addition, when the insulating board 3 is a so-called double-sided board, in which the conductors 9 on both surfaces of the insulating board 3 are connected to each other through a conductive material formed inside a through-hole by plating, the conductive material may be further adhered to the conductors 9 by this plating, and as a result, the height thereof may be further increased to approximately 40 to 70 .mu.m in some cases. On the other hand, the thickness of a thick film electrode 13 shown in FIG. 7(b) can be determined optionally to some extent, and is generally set to approximately 10 .mu.m.

Next, the difference in cross-sectional shape between the circuit pattern electrode 1 and the thick film electrode 13 will be described. The circuit pattern electrode 1 has a cross-sectional shape similar to a rectangular shape, and it is understood that the circuit pattern electrode 1 has surfaces approximately perpendicular to that of the insulating board 3 (FIG. 7(a)). On the other hand, the thick film electrode 13 has a curved cross-sectional shape primarily formed of components inclined with respect to the surface of the insulating board 3, and it is understood that the thick film electrode 13 is primarily composed of surfaces smooth with respect to the surface of the insulating board 3 (FIG. 7(b)).

Due to the difference between the circuit pattern electrode 1 and the thick film electrode 13, compared to the resistor element 8 (FIG. 7(b)) using the thick film electrodes 13 as the electrodes, the resistor element 8 (FIG. 7(a)) using the circuit pattern electrodes 1 as the electrodes has a large variation in resistance. The reason for this is that it is difficult for the former to form a resistor 2 having a uniform shape. When the variation in resistance is large, in a so-called trimming step in which adjustment is performed to obtain a desired resistance, a resistor element 8 in which an excessively long trimming groove must be formed and a resistor element 8 in which a trimming groove is not substantially necessary are both present at the same time. Although the resistances are equal to each other, when the trimming lengths are extremely different from each other as described above, due to the change in ambient environment, particularly an ambient temperature, the resistance stability cannot be obtained. That is, even when the nominal resistances are the same, in this case, resistor elements 8, in which the variation in various properties other than the resistance is large, are formed. In addition, in a stress sensor in which resistor elements 8 having trimming grooves are used as a strain gage, minute cracks around the trimming grooves will grow by the use for a long period of time, and as a result, the original resistance may not be maintained in some cases.

As described above, compared to the case in which the thick film electrodes 13 are used, when the circuit pattern electrodes 1 described above are used, the shape of the resistor 2 having a large thickness formed between the electrodes by a thick film technique such as a screen printing technique becomes unstable, and it has been, believed that there are two reasons for this problem.

The first reason is that the height of the circuit pattern electrode 1 is large as described above. For example, in the case in which a film for the resistor 2 is formed by a screen printing method, an approximately predetermined amount of a resistor paste which passed through a mask (screen) is supplied between a pair of the circuit pattern electrodes 1. Depending on various factors such as an ambient temperature, a paste temperature, and a holding time for fixing the shape of the resistor 2 obtained by firing or curing performed after screen printing, the shape of the fixed resistor 2 varies. For example, due to a high ambient temperature or the like, when the paste viscosity is low, the upper surface of the resistor 2 between a pair of the circuit pattern electrodes 1 becomes approximately flat, and as a result, a relatively stable shape is obtained. On the other hand, when a paste having a high viscosity is supplied between a pair of the circuit pattern electrodes 1, the paste is solidified by firing/curing while maintaining the original shape, which is formed when the paste is supplied, to some extent. It has been believed that this phenomenon becomes apparent when the resistor paste contains a thermosetting resin. The reason for this is believed that decrease in paste viscosity is not likely to occur even when the paste is heated. When the height of the circuit pattern electrode 1 is large, an area around the circuit pattern electrode 1 becomes a paste easy-flow region when the viscosity of the resistor paste is high. The reason for this is that the paste in the vicinity of the peak of the circuit pattern electrode 1 moves from a higher position to a lower position by its own weight.

In addition, in the case in which the film for the resistor 2 is formed by a screen printing method and in which the height of the circuit pattern electrode 1 is excessively large, when the resistor paste is allowed to pass through a mask by a squeegee, the squeegee is likely to collide against the circuit pattern electrode 1. Hence, the squeegee supplies the resistor paste through the mask in an irregular manner, resulting in the variation in amount of the resistor paste supplied through the mask and, in addition, in the deviation of the position at which the resistor paste is supplied. Accordingly, the phenomenon in which the shape of the resistor 2 formed between the circuit pattern electrodes 1 is unlikely to be stable becomes more serious.

The second reason is that the circuit pattern electrode 1 has a surface approximately perpendicular to the surface of the insulating board 3. It has been very difficult to control the resistor 2 present on the approximately perpendicular surface to have a predetermined thickness. The reason for this is that, as described above, when the paste in the vicinity of the peak of the circuit pattern electrode 1 moves from a higher position to a lower position by its own weight, it is difficult to estimate how the paste moves along the approximately perpendicular surface. In addition to the presence of the approximately perpendicular surface, the second reason described above makes the shape of the resistor 2 unstable in combination with the first reason. That is, when the height of the circuit pattern electrode 1 is small, the distance is small along which the paste in the vicinity of the peak of the circuit pattern electrode 1 described above moves by its own weight from a higher position to a lower position, and as a result, the variation in resistance caused by the difference of the thickness of the resistor 2 on the approximately perpendicular surface from that in the direction perpendicular thereto is small enough to be ignored.

This second reason is not only applied to the film formation of the resistor 2 by a thick film technique such as screen printing but is also applied to that of the film of the resistor 2 for the resistor element 8 by a thin film technique such as sputtering. The reason for this is that, for example, when sputtering is performed for the circuit pattern electrode 1 having a large height and an approximately perpendicular surface, it is difficult to control the thickness of the resistor 2 adhered to this perpendicular surface to be a predetermined value. That is, even in the film formation of the resistor 2 by a thin film technique, it is difficult to control the shape of the resistor 2 to be uniform, and as a result, the variation in resistance is liable to occur.

Accordingly, an object of the present invention is to decrease the variation in resistance of a resistor element having a resistor film formed between a pair of electrodes on a surface of the insulating board 3, the electrodes being parts of conductors obtained as the remains by partly removing a conductor layer on the surface of the insulating board. In addition, the present invention provides a stress sensor using the resistor elements described above.

DISCLOSURE OF INVENTION

Referring to FIG. 1, hereinafter, stress sensors having structures 1a to 1d of the present invention will be described. In order to achieve the objects described above, the stress sensor having structure 1a of the present invention is a stress sensor in which the direction and magnitude of a stress applied to a post 6 bonded to or integrated with a surface of an insulating board 3 can be grasped from variation in resistance of a plurality of resistor elements 8 caused by stimulation resulting from the application of the stress to the post 6. In the stress sensor described above, the resistor elements 8 are each composed of a resistor 2 formed by a screen printing method between a pair of resistor-element electrodes (circuit pattern electrodes 1); the resistor-element electrodes are connected to board terminal parts 5, provided at one end of the insulating board 3, through conductors 9; the resistor-element electrodes and the conductors 9 have a predetermined height from the surface of the insulating board 3; and for all the plurality of resistor elements 8, the arrangements of the conductors 9 and the resistor-element electrodes, in the vicinities of the respective resistor elements, are equal or similar to each other.

In addition, in order to achieve the objects described above, the stress sensor having structure 1b of the present invention is a stress sensor in which the direction and magnitude of a stress applied to the post 6 bonded to or integrated with a surface of the insulating board 3 can be grasped from variation in resistance of the plurality of resistor elements 8 caused by stimulation resulting form the application of the stress to the post 6. In the stress sensor described above, the resistor elements 8 are each composed of the resistor 2 formed by a screen printing method between a pair of the resistor-element electrodes (circuit pattern electrodes 1); the resistor-element electrodes are connected to the board terminal parts 5, provided at one end of the insulating board 3, through the conductors 9; the resistor-element electrodes and the conductors 9 or print accuracy adjusting members 7 have a predetermined height from the surface of the insulating board 3; and for all the plurality of resistor elements 8, the arrangements of the conductors 9 and the resistor-element electrodes or the print accuracy adjusting members 7, in the vicinities of the respective resistor elements, are equal or similar to each other.

According to structures 1a and 1b of the present invention, that is, for all the plurality of resistor elements, since the arrangements of the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) or the print accuracy adjustment members 7, in the vicinities of the respective resistor elements, are equal or similar to each other, the conductors 9 and the resistor-element electrodes or the print accuracy adjusting members 7, which form one stress sensor, provided on the entire insulating board 3 can be disposed in a well-balanced manner. Hence, uniform squeegee movement in screen printing of the resistor 2 and uniform squeegee shape in supplying a resistor paste between a pair of the circuit pattern electrodes 1 on the surface of the insulating board 3 can be obtained for each resistor 2. Accordingly, the variation in shape of the resistors 2 in one stress sensor can be suppressed, and as a result, the objects of the present invention can be achieved. A material for a general squeegee is a rubber-based material, and the shape thereof is easily and elastically changed. Hence, the paste is allowed to pass through opening portions of a screen.

FIG. 2(a) is a side view of a screen printing step when viewed from the side in the direction perpendicular to the squeegee movement. The state of the screen printing step, at the same timing as that shown in FIG. 2(a), is observed from between the screen and the insulating board 3 at an angle of 90.degree. rotated along the surface thereof and is shown in FIG. 2(b). In FIG. 2(b), when a pair of the circuit pattern electrodes 1, which are the resistor-element electrodes, at the right side are compared with a pair of the circuit pattern electrodes 1 at the left side, the conductors 9 and the print accuracy adjusting members 7 are not present in the vicinity of the former, and on the other side, they are present in the vicinity of the latter. Accordingly, when the resistors 2 are screen-printed between the former circuit pattern electrodes 1 and between the latter circuit pattern electrodes 1, the squeegee movement is naturally changed, and in addition, when the resistor paste is supplied onto the surface of the insulating board 3, the squeegee shape is naturally changed between the former and the latter. Hence, when structures 1a and 1b of the present invention are used, the arrangements of the conductors 9 and the print accuracy adjusting members 7 in the vicinities of the respective circuit pattern electrodes 1 can be made to be equal or similar to each other., and as a result, uniform squeegee movement in screen printing of the resistor 2 and uniform squeegee shape in supplying the resist paste onto the surface of the insulating board 3 can be obtained.

The stimulation described above is elongation or contraction of the resistor elements 8, disposed on the insulating board 3, caused by warping thereof, or compression or release of the compression of the resistor element 8 caused by the bottom surface of the post 6 without through the insulating board 3.

In general, the stress sensor comprises a control part in which electrical properties, such as the resistance described above, are for example detected and computed, thereby functioning as a stress sensor. However, in this specification, for convenience, a portion excluding the control part described above is referred to as a "stress sensor".

In addition, "the post 6 is bonded to a surface of the insulating board 3" indicates the state in which the post 6 and the insulating board 3 are different members and are fixed together with an adhesive or the like. In addition, "the post 6 is integrated with a surface of the insulating board 3" indicates the state in which the post 6 and the insulating board 3 are, for example, integrally formed. In this specification, the "outline of the bottom surface of the post 6" in the latter case indicates a portion corresponding to that represented by the "outline of the bottom surface of the post 6" in the former case.

The resistor-element electrode described above is a material having electron conductivity and being in contact with the resistor 2 and is made of part of the conductor 9 in many cases. For example, the resistor-element electrode is the circuit pattern electrode 1.

In the case in which the conductor 9 is formed by a thick film technique using a screen printing method or the like, the predetermined height described above is several micrometers to ten and several micrometers. In the case in which the conductor 9 is formed by a thin film technique using sputtering or the like, the predetermined height is approximately several tens nanometers. In addition, in the case in which a general forming technique such as a subtract method or an additive method is used for forming the conductor 9 on a printed circuit board, the predetermined height is several to several tens micrometers. In addition, since the height has a "predetermined" level, the case in which the conductor is buried in the surface of the insulating board 3 is omitted. In addition, this "predetermined" height generally means a "uniform" height. That is, it means that, in one stress sensor, a large variation in height of the conductors or the like is not present.

The "uniform" in this specification means substantial uniformity and does not means strict uniformity. For example, the variation in amount deposited by plating is ignored. The advantage obtained from the "uniform" is that the squeegee movement becomes smoother in screen printing.

In addition, concerning the term "one end", in order to avoid the misunderstanding, that is, only one side forming the insulating board 3 is regarded as the one end, generated from the narrow interpretation of the term, major portions of structures in which the board terminal parts 5 are provided at one end of the insulating board 3 are shown in FIGS. 6(a) to (g) by way of example. That is, the "one end" indicates a relatively small region along the entire periphery of the insulating board 3.

In addition, in the above "for all the plurality of resistor elements 8, and in the vicinities of", the vicinity is a region which has a large influence on the shape of the resistor 2 obtained by resistor 2 formation using a screen printing method. In forming the resistor 2 by screen printing, a region, in which a small variation in shape of the resistor 2 occurs and the influence thereof on the stress sensor properties can be ignored, is not included in the vicinity.

In addition, the above "similar" is determined in principle in accordance with the standard in which the influence on the stress sensor properties can be ignored or not. However, shapes to be compared to each other must be reasonably similar to each other. For example, the arrangements of the circuit pattern electrodes 1 or the print accuracy adjusting members 7 and the resistors 2 in the vicinities of the four resistor elements 8, shown in FIG. 1, are similar to each other in appearance on the whole.

In addition, the print accuracy adjusting members 7 described above are members other than the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) and are provided on the surface of the insulating board 3 whenever necessary, together with the conductor 9 and the resistor-element electrode, so as to obtain uniform squeegee movement in forming the resistors 2 by screen printing and uniform squeegee shape in supplying the resistor paste onto the surface of the insulating board 3 for each resistor 2. The material therefore may be a conductive material or an insulating material.

The print accuracy adjusting members 7 are preferably formed together with the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) since approximately uniform height can be obtained, and the manufacturing can be easier performed. For example, when these three members are formed by screen printing, these three members are patterned (formation of opening portions) in one screen plate. In addition, when patterned by a so-called subtract method, these three members are arranged to be obtained by one etching operation as is the case described above.

In addition, in order to achieve the objects described above, the stress sensor having structure 1c of the present invention is a stress sensor in which the direction and magnitude of a stress applied to the post 6 bonded to or integrated with a surface of the insulating board 3 can be grasped from variation in resistance of a plurality of the resistor elements caused by stimulation resulting from the application of the stress to the post 6. In the stress sensor described above, the resistor elements are composed of the resistors 2 formed by a screen printing method between pairs of the resistor-element electrodes (circuit pattern electrodes 1) disposed on a surface of the insulating board 3; the resistor-element electrodes are connected to the board terminal parts 5 provided at one end of the insulating board 3 through the conductors 9; and the resistor-element electrodes and the conductors 9 or the print accuracy adjusting members 7 have a predetermined height from the surface of the insulating board 3; and for all the plurality of resistor elements, the arrangements of the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) or the print accuracy adjusting members 7, in the vicinities of the respective resistor elements, are each formed so as to surround at least three sides of the periphery of each of the respective resistors 2.

The feature of structure 1c of the present invention as compared to structures 1a and 1b of the present invention described above is as follows. In the latter structure, for all the plurality of resistor elements, the arrangements of the conductors 9, the resistance-element electrodes (circuit pattern electrodes 1) or the print accuracy adjusting members 7, in the vicinities of the respective resistance elements, are equal or similar to each other, and on the other hand, in the former structure, for all the plurality of resistor elements 8, the arrangements of the conductors 9, the resistance-element electrodes (circuit pattern electrodes 1) or the print accuracy adjusting members 7, in the vicinities of the respective resistance elements, are each formed so as to surround at least three sides of the periphery of each of the resistors 2. The meanings of the terms, operations of the individual constituent elements, and the like of the other points are common to all the structures. In addition, it is naturally understood that the combination of structure 1c and structure 1a or 1b is not denied. For example, the four resistor elements 8 shown in FIG. 1 have structure 1a, structure 1b, and structure 1c in combination.

The above "periphery of the resistor 2" is a region in the vicinity of the end portion of the resistor, which has a large influence on the resistor 2 shape formed by resistor 2 formation using a screen printing method, and including the outside of the vicinity described above. The region described above is, for example, approximately a region in the vicinity at which the resister-element electrodes (circuit pattern electrodes 1) are in contact with the resistor 2 shown in FIG. 1 or a region including the outside of the region described above, that is, a region in the vicinity at which the conductor 9 and the print accuracy adjusting member 7 are close to the resistor 2. In forming the resistor 2 by screen printing, a region, which causes a small variation in shape of the resistor 2 so that the influence thereof on the stress sensor properties can be ignored, is not included in the region described above.

The uniform squeegee movement in forming the resistors 2 by screen printing and the uniform squeegee shape in supplying a resistor paste onto the surface of the insulating board 3 can be achieved for each resistor 2 by using structure 1c. The reason for this is that since the arrangements of the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) or the print accuracy adjusting members 7 each surround at least three sides of the periphery of each of the respective resistors 2, at least in the vicinities at which the resistors 2 are formed by printing, there are a great number of contact points between the squeegee and the conductors 9 and the resistor-element electrodes or the print accuracy adjusting members 7 with a screen provided therebetween, the contact points being continuously provided in many cases. As a result, the contact points described above contribute to the improvement in uniformity of the squeegee movement and the squeegee shape in supplying the resistor paste onto the surface of the insulating board 3 for each resistor 2.

In addition, in order to achieve the objects described above, the stress sensor having structure 1d of the present invention is a stress sensor in which the direction and magnitude of a stress applied to the post 6 bonded to or integrated with a surface of the insulating board 3 can be grasped from variation in resistance of a plurality of the resistor elements 8 caused by stimulation resulting from the application of the stress to the post 6. In the stress sensor described above, the resistor elements 8 are composed of the resistors 2 formed by a screen printing method between pairs of the resistor-element electrodes (circuit pattern electrodes 1) disposed on a surface of the insulating board 3, the circuit pattern electrodes 1 are connected to the board terminal parts 5 provided at one end of the insulating board 3 through the conductors 9, and the circuit pattern electrodes 1 and the conductors 9 or the print accuracy adjusting members 7 have a predetermined height from the surface of the insulating board 3. In addition, the circuit pattern electrodes 1 and the conductors 9 or the print accuracy adjusting members 7 are disposed so as to intermittently or continuously surround all the plurality of resistor elements.

The feature of structure 1d of the present invention as compared to structure 1c of the present invention described above is as follows. In the latter structure, the conductors 9 and the resistor-element electrodes (circuit pattern electrodes 1) or the print accuracy adjusting members 7 are provided so as to surround the respective resistor elements, and on the other hand, in the former structure, the conductors 9 and the resistor-element electrodes or the print accuracy adjusting members 7 are provided so as to collectively surround the plurality of resistor elements. The meanings of the terms, operations of the individual constituent elements, and the like of the other points are common to all the structures. In addition, it is naturally understood that the combination of structure 1d and structures 1a and/or structure 1b and/or structure 1c is not denied. The combination described above is more preferable since the advantages thereof may be favorably enhanced.

In these structures 1a to 1d described above, as the constituent elements of the stress sensors, the resistor-element electrodes (circuit pattern electrodes 1), the conductors 9, or the print accuracy adjusting members 7 are preferably formed by adhering a metal foil to the surface of the insulating board 3 followed by etching treatment performed for unnecessary parts of this metal foil. Compared to the case in which the resistor-element electrodes, the conductors 9, or the print accuracy adjusting members 7 are formed on the surface of the insulating board 3 by a general thick film or thin film technique such as screen printing or sputtering, the height of the resistor-element electrodes, the conductors 9, or the print accuracy adjusting members 7 from the surface of the insulating board 3 is large as described above. The reason for this is that the thicknesses thereof depend on the thickness of the metal foil described above, or that in an electroless plating step in which a conductive film is formed on inner walls of thorough-holes, the conductive film is also deposited on the metal foil. The thickness of the current metal foil is approximately 9 to 36 .mu.m, and a foil having a thickness of approximately 18 .mu.m is generally used. When the electroless plating step described above is performed, the height of the circuit pattern electrodes 1, the conductors 9, or the print accuracy adjusting members 7 from the surface of the insulating board 3 is generally 30 to 50 .mu.m. When the circuit pattern electrodes 1, the conductors 9, or the print accuracy adjusting members 7, having a large height from the surface of the insulating board 3, are used, it is particularly difficult to obtain uniform squeegee movement in forming the resistors 2 by screen printing and uniform squeegee shape in supplying the resistor paste onto the surface of the insulating board 3 for each resistor 2, and hence, the application of the present invention can significantly contribute to the improvement in stress sensor properties.

This significant contribution can be obtained when the height of the resistor-element electrodes (circuit pattern electrodes 1), the conductors 9, or the print accuracy adjusting members 7 is 10 .mu.m or more, more significant contribution can be obtained when the height is 20 .mu.m or more, and even more significant contribution can be obtained when the height is 30 .mu.m or more.

In addition, in order to achieve the objects described above, a method for manufacturing a stress sensor, according to the present invention, is a method for manufacturing a process sensor in which the direction and magnitude of a stress applied to the post 6 bonded to or integrated with a surface of the insulating board 3 can be grasped from variation in resistance of a plurality of the resistor elements 8 caused by stimulation resulting from the application of the stress to the post 6. The method described above comprises a first step of forming the circuit pattern electrodes 1, the board terminal parts 5, and the conductors 9 so that the resistor-element electrodes (circuit pattern electrodes 1) are connected to the board terminal parts 5 provided at one end of the insulating board 3 through the conductors 9; a second step of providing an insulating film on a surface of the insulating board 3 so as not to cover at least the circuit pattern electrodes 1; and a third step of forming the resistors 2 by a screen printing method between pairs of the circuit pattern electrodes 1 provided on the surface of the insulating board 3, wherein the first step, the second step, and the third step are performed in that order.

The first step described above can be realized by a screen printing method in which a conductive paste is applied onto the surface of the insulating board 3 formed of alumina or the like; a so-called subtract method in which a copper foil is adhered to a molded plate of a glass fiber filled epoxy resin, followed by etching to remove areas other than those necessary as the conductors 9; or a so-called additive method, a plating method, or the like in which the conductors 9 are deposited on necessary areas.

In order to obtain the uniform squeegee movement in forming the resistors 2 by the screen printing in the subsequent third step and the uniform squeegee shape in supplying the resistor paste onto the surface of the insulating board 3 for each resistor 2, the second step described above is a step of adjusting the height of the resistor-element electrodes, the board terminal parts 5, and the conductors 9 from the surface of the insulating board 3. That is, as described above, when the height of the resistor-element electrodes, the conductors 9, or the print accuracy adjusting members 7 from the surface of the insulating board 3 is larger, in other words, when the difference in height of a surface of a workpiece, which is to be printed and to be brought into contact with a squeegee for screen printing with a screen provided therebetween, is larger, it becomes more difficult to obtain the uniform squeegee movement. Accordingly, in order to decrease or eliminate the difference in height described above, the level of the surface of the insulating board 3 is increased so as to be closer to the height of the resistor-element electrode or the conductor 9 or to exceed the height thereof by forming the insulating film over the conductors 9.

In the case in which a stress applied to the post 6 warps the insulating board 3, the resistor elements 8 are then warped thereby, and the stress sensor detects the variation in resistance of the resistor elements 8 thus warped, the insulating film described above is preferably formed of a material softer than the insulating board 3. The reason for this is that when the insulating film is a material having high rigidity as compared to that of the insulating board 3, the warping of the insulating board 3 may be inhibited in some cases. For example, when the material for the insulating board 3 is a molded body of a glass fiber filled epoxy resin, a cured silicone resin paste or the like may be preferably used. In this case, for example, the paste is applied by screen printing or the like so as to cover the surface of the insulating board 3 and the conductors 9 provided thereon. Accordingly, the paste on the conductors 9, provided at the higher position, flows to the surface of the insulating board 3 located at the lower position and is then cured by heating to form an insulating film, and hence the difference in height described above can be decreased or eliminated. In this step, attention must be paid so that the paste is not applied onto the surfaces of the resistor-element electrodes (circuit pattern electrodes 1). The reason for this is that the presence of a material which may interfere with the electrical connection with the resistors 2 formed in the subsequent step is avoided. In this specification, the surface of the resistor-element electrodes includes the top surface and/or the side surfaces thereof. Hence, when the top surface of the resistor-element electrode is exposed, of course, the insulating film may be disposed in some cases between the electrodes at which the resistor 2 is to be provided.

Means for not applying the paste on the surfaces of the circuit pattern electrodes 1 may comprise, for example, performing masking treatment in which the contact between the paste and the circuit pattern electrodes 1 is inhibited, and removing the mask after the paste is cured. Alternatively, for example, after the paste is applied onto the surfaces of the circuit pattern electrodes 1 and curing thereof, the paste is removed by polishing the surfaces of the circuit pattern electrodes 1.

A first structure of the resistor element 8 of the present invention, which achieves the objects described above, comprises: electrodes (circuit pattern electrodes 1) composed of parts of the conductors 9 on a surface of the insulating board 3 obtained by partly removing a conductive layer on the surface as remains or by an additive method; and the resistor 2 formed by film formation between a pair of the circuit pattern electrodes 1 on the surface of the insulating board 3. In the structure described above, the ratio L/h of the distance (L) between the pair of the electrodes to the electrode height (h) is 30 or more.

In FIG. 9, positions at which the distance (L) between the electrodes and the electrode height (h) are measured are shown. As means for obtaining a ratio L/h of 30 or more, for example, there may be mentioned means for decreasing the electrode height (h) and means for increasing the distance (L) between the electrodes. In addition, of course, the means described above may be used in combination.

By the means for decreasing the electrode height (h), the variation in resistance of the resistor elements 8 caused by the first reason and the second reason described above can be decreased. In addition, when a ratio L/h of 30 or more is obtained by this means, even in the resistor elements 8, each comprising the electrodes (circuit pattern electrodes 1) composed of parts of the conductors 9 obtained by partly removing the conductive layer on the surface as the remains or by an additive method; and the resistor 2 formed by film formation between the pair of the circuit pattern electrodes 1 on the surface of the insulating board 3, the variation in resistance can be decreased.

When the electrode height (h) is decreased, in the structure in which the top surface of the circuit pattern electrode 1 is at the same level of the surface of the insulating board 3 or in the structure in which the top surface of the circuit pattern electrode 1 is located at a lower level than the surface of the insulating board 3, said h becomes 0 or less, and as a result, the ratio L/h cannot be 30 or more. However, even in the case described above, since the same advantage as that of the first structure described above can be obtained, in the present invention, the case in which said h is 0 or less is also included in the structure of the present invention.

In addition, in the case in which a ratio L/h of 30 or more is obtained by the means for increasing the distance (L) between the electrodes, due to the first and the second reasons described above, even when the variation in shape of the resistor 2 in the vicinities of the circuit pattern electrodes 1 occurs, the variation can be decreased so as to be ignored. That is, in each of the resistor 2 provided between the pair of the circuit pattern electrodes 1, when the ratio of part of the resistor 2 provided at a relatively distant position from the surfaces of the circuit pattern electrodes 1 and having a relatively reproducible shape is increased, the variation in resistance of the resistor elements 8 can be decreased. In other words, among the factors determining the resistance, including an unstable factor (part of the resistor 2 provided in the vicinities of the circuit pattern electrodes 1) and a stable factor (part of the resistor 2 provided at a distant from the surfaces of the circuit pattern electrodes 1 and having a relatively reproducible shape), when the ratio of the stable factors is increased, the variation in resistance of the resistor elements 8 can be suppressed.

In the resistor element 8 having the first structure of the present invention, the technical meaning in which the ratio L/h is set to 30 or more is based on the experimental result. When the ratio L/h was set to approximately 24, the variation in resistance of the resistor elements 8 was in a range of .+-.17% (n=30). Hence, in the case in which the ratio L/h was set to approximately 30, the variation in resistance of the resistor elements 8 was in a range of .+-.9% (n=30). In addition, when the ratio L/h was set to approximately 40, 45, 50, 55, and 60, the variation in resistance is slightly decreased in that order; however, the variation described above is not so significantly different from that obtained when the ratio L/h was set to approximately 30. This is the process and the reason for determining that "the ratio L/h is 30 or more".

A method for manufacturing the resistor element having the first structure of the present invention, for achieving the objects of the present invention, comprises a fourth step of obtaining the conductors 9 on a surface of the insulating board 3, a fifth step of positively adjusting the height of parts or the entirety of the conductors 9, and a sixth step of, by using parts of the conductors 9 as electrodes, forming the resistor 2 by film formation between a pair of the electrodes provided on the surface of the insulating board 3, in which the fourth to the sixth steps are performed in the numerical order. In the fifth step of the method described above, the ratio L/h of the distance (L) between said pair of the electrodes to the height (h) of the conductors 9 is set to 30 or more, or said h is set to 0 or less.

As described above, the fourth step is a step, for example, of obtaining the conductor 9 layer on the surface of the insulating board 3 by removing the conductor 9 layer on the surface thereof or by an additive method.

The above fifth step is performed, for example, by a press step of pressing the surface of the insulating board 3. This step is a step of obtaining a ratio L/h of 30 or more by forcedly pressing the circuit pattern electrodes 1, which is formed to have a large height, into the insulating board 3 or deforming the circuit pattern electrodes 1 itself so that the electrode height (h) is finally adjusted to be smaller. As this press step, for example, there may be mentioned a press step of pressing the entire surface of the insulating board 3 by roller press or press with a pressure using a flat plate having no concave portions as a die, or a press step of pressing only parts of the insulating board 3 corresponding to the circuit pattern electrodes 1.

In addition, the above fifth step may be a step, for example, of polishing the surface of the insulating board 3 or performing acid treatment thereof. This step is a step of finally decreasing the height (h) of the circuit pattern electrodes 1 through adjustment by mechanical polishing, for example, using an abrasive paper or by immersing the insulating board 3 in an acidic solution for dissolution of a metal so that the ratio L/h is set to 30 or more. In this step, when the insulating board 3 is used having the structure in which conductors 9 patterns on two surfaces of the insulating board 3 are connected to each other through a conductive material provided in through-holes, the through-hole portions are preferably masked so as not to be brought into contact with the acidic solution for preventing the conductive material in the through-holes from being excessively dissolved.

When the first structure of the resistor element 8 of the present invention comprises a potion at which circuit patterns on two surfaces of the insulating board 3 are connected to each other with a conductive material provided in a through-hole, and the resistor 2 formed by film formation between a pair of electrodes on the surface of the insulating board 3, the electrodes formed of parts of the conductors 9 on the surface thereof, the electrode height (h) may be particularly increased in some cases, and hence the present invention is preferably used. The reason the electrode height (h) may be increased is that in a manufacturing method of a so-called double-sided circuit board, in order to form conductive layers on inner walls of through-holes of the insulating board 3 so that wires on two surfaces thereof are connected to each other, an electroless plating step is performed. As a result, the electroless plating layer thus formed is also deposited on portions which are to be formed into the circuit pattern electrodes 1.

The above fifth step including the plating step as described above may be a plating step of plating inside the through-holes formed in the insulating board 3 after the pair of the electrodes on the surface thereof is covered. Next, the electrode height (h) is adjusted to be small, and the ratio L/h is set to 30 or more.

In the present invention, of course, at least two of the fifth steps described by way of example may be used in combination.

In addition, in a second structure of the stress sensor of the present invention, the post 6 is bonded to or integrated with one of surfaces of the insulating board 3 forming all the resistor elements 8 having the first structure of the present invention, and the direction and magnitude of a stress applied to the post 6 is grasped from the variation in resistance of the resistor elements 8 resulting from the application of the stress.

In the stress sensor described above, for example, as shown in FIGS. 1 and 8, the resistor elements 8 are provided on two lines, which are along a surface of the insulating board 3 forming the resistor elements 8 and perpendicularly intersect each other at the center of a sensor effective region of a surface of the insulating board 3, and are provided at substantially the same distance from the center, and the post 6 is bonded to or integrated with a surface of the insulating board 3 so that the center thereof substantially coincides with the center of the bottom surface of the post 6. Accordingly, the direction and magnitude of a stress applied to the post 6 is grasped from the variation in resistance of the resistor elements 8 caused by elongation, contraction, or compression thereof resulting from the application of the stress.

Referring to FIG. 8, an example of the structure of the stress sensor according to the present invention will be further described. The insulating board 3 is formed, for example, of a glass fiber filled epoxy resin. On the bottom surface of the insulating board 3, four pairs of circuit pattern electrodes 1 are provided, and the resistors 2 are provided between the respective pairs of circuit pattern electrodes 1, thereby forming the resistor elements 8. The resistor elements 8 are provided on two lines, which are along the surface of the insulating board 3 and intersect perpendicularly to each other, and are provided at substantially the same distance from the intersection described above. To the top surface of the insulating board 3, the post 6 is fixed with an adhesive or the like, in which the bottom surface of the post has an approximately square outline. In this step, the center of the bottom surface of the post 6 is provided so as to substantially coincide with the center of the insulating board 3.

In addition, L-shaped holes 10 are formed in the insulating board 3 so that the corners of the L-shapes face the center of the insulating board 3. These holes 10 serve so as to allow the insulating board 3 to be easily warped by a stress applied to the post 6 and to efficiently propagate the stress to the individual resistor elements 8. That is, in the case in which a stress is applied to the post 6 when the holes 10 are not provided, in addition to insufficient warpage of the insulating board 3, the stress applied in an optional direction may also be propagated to the resistor element 8 provided in a different direction therefrom in some cases, and hence the holes 10 are preferably formed.

In addition, trimmable chip resistors 11 which are to be connected to the respective resistor elements 8 in series are provided on the top surface of the insulating board 3. The resistor elements 8 on the bottom surface of the insulating board 3 and the trimmable chip resistors 11 on the top surface of the insulating board 3 are electrically connected through through-holes (via holes), not shown in the figure, formed in the insulating board 3. When it is difficult to adjust the resistance of each resistor element 8 in a predetermined range, the trimmable chip resistor 11 is used so that the sum of the resistances of the resistor element 8 and the trimmable chip resistor 11 is adjusted in a predetermined range by trimming the trimmable chip resistor 11 using a laser trimmer or the like. The electrical connection state of the trimmable chip resistors 11 and the resistor elements 8 is shown in FIG. 4 by way of example. Electrical signals from the stress sensor are output through the board terminal parts 5.

Support holes 12 are used for fixing the stress sensor to a housing of an electronic device or the like. In the fixed state obtained thereby, the peripheral portions of the insulating board 3 outside the holes 10 become non-deformable portions which are not substantially deformed even when a stress is applied to the post 6, and the insides of the holes 10 become deformable portions which are deformed when a stress is applied to the post 6 so as to elongate and contract the resistor elements 8. The trimmable chip resistors 11 are preferably provided in the non-deformable portions so that the resistances thereof are not varied by the influence of the deformation of the insulating board 3.

The meanings of the terms used for the stress sensor having the second structure are equivalent to those used for the stress sensors having structures 1a to 1d. In addition, of course, the combination of the second structure and structures 1a to 1d is not denied. The combination described above is more preferable since the advantages thereof may be favorably enhanced.

In the structure shown in FIG. 8, the holes 10, the support holes 12, and the trimmable chip resistors 11 are particularly optional constituent elements (not essential elements) of the s