JP2015017848A - Dynamic quantity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic quantity measuring device in which a strain measurement range on a compression side is expanded.SOLUTION: A dynamic quantity measuring device includes: a sensor chip that has a plurality of piezoresistive elements and electrode pads formed on a surface of a semiconductor substrate; a lead wiring part that includes wiring electrically connected with the electrode pads; and a metal plate that is bonded to a rear surface of the sensor chip. A rear surface of the metal plate has a protrusion in a part within a region opposed to the rear surface of the sensor chip.

Description

  The present invention relates to a mechanical quantity measuring apparatus using a semiconductor strain sensor capable of measuring strain and stress of a structure.

  Patent Document 1 describes a strain detection sensor in which a sensor chip (strain detection element) made of a silicon semiconductor is joined to a glass base using low melting point glass.

  The most popular method for measuring the strain and stress of a structure is a method using a strain gauge. A strain gauge has a structure in which a wiring pattern of a Cu-Ni alloy or Ni-Cr alloy metal thin film is formed on a polyimide or epoxy resin film and a lead wire is provided. Adhere with and use. The amount of strain can be calculated from the change in resistance value resulting from the deformation of the metal thin film.

  On the other hand, development of semiconductor strain sensors using semiconductors is progressing as a method for measuring strain with higher accuracy. This is a device that uses a semiconductor piezoresistor formed by doping an impurity in a semiconductor such as silicon (Si) instead of a metal thin film. A semiconductor strain sensor has a resistance change rate with respect to strain as large as several tens of times that of a strain gauge using a metal thin film, and can measure a minute strain. In addition, since the resistance change is small in the metal thin film strain gauge, an external amplifier for amplifying the obtained electric signal is required. Since the semiconductor strain sensor has a large resistance change, the obtained electrical signal can be used without using an external amplifier, and it is also possible to build an amplifier circuit on the semiconductor chip of the semiconductor strain sensor. It is expected that the convenience of use and usage will be greatly expanded.

  For the purpose of improving the usability of such a strain sensor, development of a metal plate module in which a semiconductor strain sensor is joined to a metal plate is being promoted. FIG. 1 is a schematic diagram when the metal plate module 4 and the metal plate module are attached to the object 5 to be measured. Since the metal plate module 4 can be attached by various methods such as (a) bonding with the adhesive 6, (b) screwing with the screw 7, and (c) welding at the welded portion 8, the usability for the user is improved. it can. This metal plate module has a configuration in which a sensor chip 1 which is a semiconductor strain sensor is joined to a metal plate 3 via an adhesive or a solder material. In FIG. 2, the schematic diagram of the joining process of the sensor chip 1 and the load state of a metal plate module is shown. The chip is mounted in a state heated to a high temperature, and then the bonding is completed by cooling to room temperature. The linear expansion coefficient (hereinafter referred to as α) of the sensor chip 1 made of silicon is about 3 ppm / ° C., and α of the metal plate is generally larger than α of the sensor chip. For example, α of the stainless steel material is about 16 ppm / ° C., and α of the aluminum alloy material is about 23 ppm / ° C. Therefore, in the room temperature state where the joining is completed, residual strain of shear deformation is generated in the joining material 2 due to a large contraction of the metal plate side.

  Next, the measurable strain range in the metal plate module will be described. As shown in FIG. 3, when a load strain is applied to the metal plate module, the sensor output increases in proportion to the load strain. However, when a certain strain value or more is applied, the behavior of the sensor output becomes nonlinear due to the plastic deformation of the bonding material. It is desirable that the region where the linearity is maintained (hereinafter referred to as a strain measurement range) be as wide as possible.

  However, as described above, the initial residual strain is generated in the metal plate module. Here, as shown in FIG. 2, when compressive strain is applied to the metal plate module, the shear deformation at the end of the bonding material is in the same direction as the shear deformation of the initial residual strain.

  On the other hand, when a tensile strain is applied, the shear deformation at the end of the bonding material is in the opposite direction to the shear deformation of the initial residual strain. Therefore, the strain measurement range on the compression side is considered to be smaller by the initial residual strain than the strain measurement range on the tension side. Since the user often uses the strain measurement range on the tension side and the compression side on the same level, the fact that only the strain measurement range on the compression side is small reduces the convenience for the user.

JP 2001-272287 A

Accordingly, an object of the present invention is to provide a mechanical quantity measuring device in which the strain measurement range on the compression side is expanded.

A mechanical quantity measuring device according to an aspect of the present invention includes a surface, a plurality of piezoresistive elements formed on the surface side, a plurality of electrode pads electrically connected to the piezoresistive elements, and an opposite side of the surface. A sensor chip including a back surface positioned, a metal plate bonded to the back surface via a bonding material, and a surface opposite to a surface of the metal plate on which the sensor chip is bonded, corresponding to the back surface. A protrusion formed at a position;
It is the mechanical quantity measuring device characterized by having.

  A sensor chip comprising a front surface, a plurality of piezoresistive elements formed on the front surface side, a plurality of electrode pads electrically connected to the piezoresistive elements, and a back surface located on the opposite side of the surface; A metal plate bonded to the back surface via a bonding material; and a convex curved portion formed on a position opposite to the surface of the metal plate on which the sensor chip is bonded, corresponding to the back surface; A mechanical quantity measuring device characterized by comprising:

  According to the present invention, the amount of compressive strain that can be measured by the mechanical quantity measuring device can be increased.

It is the schematic diagram which showed the attachment method of the metal plate module. It is a schematic diagram which shows the deformation | transformation state at the time of the sensor chip joining process and module load of a metal plate module. It is a figure which shows the relationship between a load distortion and a sensor output. 1 is a plan view of a mechanical quantity measuring device according to a first embodiment of the present invention. It is an expanded sectional view along the AA line of FIG. It is a top view which shows typically the structure of the surface side of the sensor chip shown in FIGS. It is a top view which shows the state by which the mechanical quantity measuring device which is the 1st Example of this invention was adhere | attached and fixed on the to-be-measured object. It is sectional drawing along the AA line of FIG. It is a top view which shows the state by which the mechanical quantity measuring apparatus which is the 2nd Example of this invention was attached on the to-be-measured object. It is sectional drawing along the AA line of FIG. It is sectional drawing of the mechanical quantity measuring apparatus which is the 3rd Example of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiment is described

In all the drawings for the purpose, members having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
[Example 1]
First, the basic configuration of the mechanical quantity measuring device of the present embodiment will be described. FIG. 4 is a perspective plan view of the mechanical quantity measuring device according to the present embodiment. FIG. 5 is a cross-sectional view taken along the line AA in FIG. In FIG. 4, in order to show the internal structure of the sealing resin 12, the outline of the sealing resin 12 is indicated by a two-dot chain line, and the internal structure that has passed through the sealing resin 12 is shown. As shown in FIGS. 4 and 5, the metal plate module that is the mechanical quantity measuring device of the present embodiment includes a sensor chip 1 that is a semiconductor strain sensor, and a wiring portion 11 (electrically connected to the sensor chip 1 ( A flexible wiring board, a glass epoxy substrate, etc.), a metal plate 3 on which the sensor chip 1 is mounted via the bonding material 2, and a sealing resin 12 for sealing the sensor chip 1.

  6a and 6b are plan views schematically showing the configuration of the surface side of the sensor chip 1 shown in FIGS. The sensor chip 1 includes a front surface (main surface) 1a and a back surface (main surface) 1b located on the opposite side of the front surface 1a as shown in FIGS. 6a and 6b. A metal film is formed on the back surface 1b of the sensor chip 1, and the back surface 1b is covered with the metal film. This metal film is composed of a laminated film (metal laminated film) in which chromium, nickel, gold (Cr, Ni, Au) are sequentially laminated from the semiconductor substrate side, for example, and can be formed by, for example, a sputtering method. Thus, by covering the back surface 1b of the sensor chip 1 with the metal film, the bonding strength with the metal bonding material 2 such as solder can be improved. Further, the front surface 1a and the back surface 1b each form a quadrilateral (quadrangle), and in the example shown in FIGS. 6a and 6b, for example, each side has a length of about 2 mm to 3 mm. In addition, the sensor chip 1 includes a plurality of resistance elements 15 (piezoresistance elements) formed in the sensor region 14 located in the center portion on the surface 1a side.

  In addition, the sensor chip 1 is electrically connected to a plurality of resistance elements 15 (piezoresistive elements) formed in an input / output circuit region located on the peripheral side of the sensor region 14 on the surface 1a side. An electrode (pad, electrode pad 9) is provided. The plurality of resistance elements 15 are constituted by impurity diffusion regions in which, for example, an element formation surface of a silicon substrate having a (100) plane is doped and diffused. For example, the sensor chip 1 electrically connects four resistance elements 15 to form a Wheatstone bridge circuit, and measures a resistance change of the resistance element 15 due to the piezoresistance effect to detect strain. Circuit).

  The detection circuit is connected to the plurality of electrode pads 9 via a plurality of wirings. The plurality of electrode pads 9 are input / output terminals of the sensor chip 1. For example, a terminal Vcc that supplies a power supply potential (first power supply potential) to the sensor chip 1 and a reference potential (second power supply potential) are supplied. A terminal GND and a terminal SIG for outputting a detection signal are included. Further, the layout of the plurality of resistance elements 15 constituting the detection circuit is not limited to the mode shown in FIG. 6, but the following configuration is adopted in the present embodiment. That is, when the semiconductor substrate (for example, a silicon substrate made of silicon (Si)) provided in the sensor chip 1 is a single crystal (silicon single crystal), the extending direction (longitudinal direction) of the plurality of resistance elements 15 constituting the detection circuit. Respectively coincide with the <110> direction or <100> direction of a semiconductor substrate having a (100) plane. For example, in the example shown in FIG. 6a, the semiconductor substrate (silicon substrate) provided in the sensor chip 1 has a crystal orientation in the <110> direction of the silicon single crystal (the X direction and the Y direction orthogonal to the X direction in FIG. 6a). Four p-type diffusion regions (regions doped with impurities whose conductivity type is p-type) are formed so that a current flows along. In other words, in the sensor chip 1, four resistance elements 15 are formed by doping p-type impurities at four locations so as to extend along the crystal orientation in the <110> direction of the silicon single crystal of the silicon substrate. .

  In the example shown in FIG. 6b, the semiconductor substrate (silicon substrate) included in the sensor chip 1 has a crystal orientation in the <100> direction of the silicon single crystal (the X direction and the Y direction orthogonal to the X direction in FIG. 6b). Four n-type diffusion regions (regions doped with impurities whose conductivity type is n-type) are formed so that a current flows along. In other words, in the sensor chip 1, four resistance elements 15 are formed by doping n-type impurities at four locations so as to extend along the crystal orientation in the <100> direction of the silicon single crystal of the silicon substrate. .

  As shown in FIGS. 6a and 6b, the sensor chip in which the extending directions of the plurality of resistance elements 15 constituting the detection circuit coincide with the <110> direction or the <100> direction of the semiconductor substrate having the (100) plane, respectively. 1 can output, for example, the difference between the strain in the X direction and the strain in the Y direction shown in FIGS. 6a and 6b. Specifically, the difference between the strain in the X direction and the strain in the Y direction can be output as a potential difference from the terminal SIG shown in FIGS. 6a and 6b. As described above, the measurement method that outputs the difference between the strain in the X direction and the strain in the Y direction is advantageous from the viewpoint of reducing the influence of the thermal strain applied to the sensor chip 1.

  That is, as shown in FIG. 1, the sensor chip 1 is fixed on the object to be measured via a plurality of members (in the case of FIG. 5, the metal plate 3 and the bonding material 2). The thermal distortion resulting from the difference of the linear expansion coefficient of each member arises. Since this thermal strain is a noise component different from the strain to be measured, it is preferable to reduce the influence of thermal strain.

  Here, as shown in FIGS. 6a and 6b, when the planar shape of the sensor chip 1 is a square, the influence of the thermal strain is approximately the same in the X direction and the Y direction. For this reason, for example, when detecting the strain generated in the X direction, if the difference between the strain in the X direction and the strain in the Y direction is output, the strain amount due to the thermal strain is canceled, and the strain to be measured. Can be selectively detected.

That is, if the sensor chip 1 is used, the influence of thermal strain can be reduced, so that variation in strain value due to changes in environmental temperature can be reduced. In addition, since each member such as the resistance element 15 and the electrode pad 9 constituting the sensor chip 1 can be formed by applying a known semiconductor device manufacturing technique, the elements and wirings can be easily miniaturized. Moreover, manufacturing efficiency can be improved and manufacturing cost can be reduced.

  Next, the bonding material 2 will be described. The bonding material 2 is provided so as to cover the entire back surface of the sensor chip 1 and a part of the side surface of the sensor chip 1. In other words, the peripheral edge of the bonding material 2 may extend to the outside of the side surface of the sensor chip 1 to form a fillet. From the viewpoint of fixing the sensor chip 1 and the metal plate 3, the bonding material 2 is not limited to a metal material, and for example, a resin adhesive such as a thermosetting resin can be used.

  Next, as shown in FIG. 4, a wiring portion 11 including a plurality of wirings electrically connected to the plurality of electrode pads 9 of the sensor chip 1 is fixed on the metal plate. The wiring 11 has a configuration in which a wiring portion which is a plurality of metal patterns is sealed in a resin film, and a part of the plurality of wirings is exposed in an opening provided in a part of the resin film. The exposed portion constitutes a plurality of terminals. In the example shown in FIG. 4, the plurality of electrode pads 9 of the sensor chip 1 and the plurality of terminals of the wiring portion are electrically connected via a plurality of Au wires 10 (conductive members). The wire 10 is, for example, a gold wire (Au wire) having a wire diameter of about 10 μm to 200 μm, and is sealed with a sealing resin 12. By covering the wire 10 with the sealing resin 12, a short circuit between adjacent wires can be prevented. Further, one end of the wiring portion is fixed to a metal plate as shown in FIG. 4, but a connector (not shown) is formed on the other end, for example, a control circuit (not shown) for controlling strain measurement. Is omitted). In FIG. 4, the wiring portion and the wire are described separately, but a plurality of wires may be considered as the wiring portion. Moreover, the wiring part should just be able to transmit an input-output current between the sensor chip 1 and the external apparatus which is not shown in figure, and is not limited to the aspect shown in FIG.

  Next, the metal plate will be described. The constituent material of the metal plate is not particularly limited, but the material of the metal plate is preferably the same as the material of the object to be measured. This is to suppress the occurrence of thermal strain due to the α difference between the object to be measured and the metal plate when the environmental temperature fluctuates. Therefore, as a kind of the metal plate, iron (Fe), copper (Cu), aluminum (Al), so-called stainless steel (iron alloy containing chromium element) or so-called often used as the material of the object to be measured, or so-called Made of duralumin (aluminum alloy).

  Further, as shown in FIG. 5, the metal plate 3 is disposed on both sides of the region (sensor chip mounting region 31) on which the sensor chip 1 is mounted (opposite the back surface 1 b of the sensor chip 1) and the region 31. And a sensor chip non-mounting region 32, and a protrusion 13 is provided in a part of the region 31. The positions 16 at both ends of the protrusion are present inside the positions 17 at both ends of the sensor chip. The effect of having such a dimensional relationship will be described later. On the other hand, the upper surface side is flattened at the same height. The metal plate 3 can be formed by, for example, etching, machining, or pressing on a flat plate.

  Further, as shown in FIG. 4, the four corners (four corners) of the metal plate 3 form an arc shape in plan view. When the metal plate module is attached to the object to be measured with an adhesive, the four corners of the metal plate 3 are most likely to concentrate stress when strain is applied to the object to be measured 5. Therefore, as shown in FIG. 4, it is preferable to process the four corners so as to form an arc shape. As a result, stress can be dispersed, so that the strain concentration of the adhesive layer can be relaxed around the corners, and the occurrence of peeling or cracking can be suppressed. Moreover, the stress which generate | occur | produces in the metal plate 3 itself can be relieve | moderated by making a corner | angular part into circular arc shape. For this reason, fatigue failure of the metal plate 3 can be suppressed.

  Next, FIG. 7 is a perspective plan view showing a state in which the mechanical quantity measuring device of the present embodiment is bonded and fixed on the object to be measured. FIG. 8 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 8, in the metal plate module 4, the lower surface (mounting surface 3b) side of the metal plate 3 is bonded and fixed to the measurement object via the adhesive 6, and the strain applied to the measurement object 5 is It is transmitted to the sensor chip 1 via the adhesive 6 and the metal plate 3 and measured. Next, when the metal plate module 4 is attached to the object to be measured with an adhesive, both ends of the metal plate are usually bonded by pressing and heating from above. This is because the adhesive strength of the adhesive can be improved by applying pressure.

  Here, since the protrusions 13 are present on the back side of the metal plate 3, the metal plate module is warped upward in a convex direction by pressurization during bonding. Further, finally, bonding is performed in a state in which a convex warpage deformation has occurred. Therefore, the shearing strain resulting from the deformation of the metal plate 3 is also generated in the bonding material 2. As described above, since the residual shear strain due to the large shrinkage of the metal plate is generated in the bonding material 2, the measurement strain range on the compression side is small. However, if the structure of the present embodiment is used, the residual strain generated in the bonding material 2 can be reduced in the initial state where the module is attached. That is, it is possible to expand the measurement strain range on the compression side. It should be noted that the user need only perform a normal pasting operation without being particularly conscious in the module mounting process.

Further, when the positions 16 at both ends of the protrusion 13 are not inside the positions 17 at both ends of the chip, there is a possibility that tensile strain cannot be applied to the metal plate in contact with the back side of the bonding material. Therefore, the positions 16 at both ends of the protrusion 13 need to be located inside the positions 17 at both ends of the chip.
[Example 2]
FIG. 9 is a perspective plan view showing a state in which the mechanical quantity measuring device according to the present embodiment is fixed to the object to be measured by screw tightening. FIG. 10 is a cross-sectional view taken along line AA in FIG. As shown in FIG. 10, the metal plate module 4 is attached to the object to be measured 5 with screws 7 through holes provided at both ends of the metal plate 3. In the case of this structure, the same effect as the case of fixing with the adhesive of Example 1 can be obtained. In other words, the metal plate module 4 is warped upward in the convex direction due to the screw tightening. Therefore, the joining material 2 is also subjected to a shear strain due to the deformation that the metal plate 3 extends. By this deformation, the initial residual strain of the bonding material 2 is reduced, so that the measurement strain range on the compression side of the metal plate module can be expanded. It should be noted that the user need only perform a normal pasting operation without being particularly conscious in the module mounting process.
[Example 3]
FIG. 11 is a diagram showing a cross-sectional structure of the mechanical quantity measuring device according to the present embodiment. The metal plate 3 has a structure having a downwardly bent portion in the region 31 between both ends of the sensor chip (curved portion 18 on the back side of the metal plate).
It has become. Further, the thickness of the metal plate in the region 31 is larger than the thickness of the metal plate in the region 32. When this metal plate module is fixed to an object to be measured using an adhesive, it is considered that the same effects as those described in Example 1 can be obtained. Further, when holes are provided at both ends of the metal plate module and the object to be measured is screwed, it is considered that the same effect as described in Example 2 can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Sensor chip, 1a ... Front surface, 1b ... Back surface, 2 ... Bonding material, 3 ... Metal plate, 3b ... Mounting surface, 4 ... Metal plate module, 5 ... Measuring object, 6 ... Adhesive, 7 ... Screw, 8 DESCRIPTION OF SYMBOLS ... Welding part, 9 ... Electrode pad, 10 ... Au wire, 11 ... Wiring part, 12 ... Sealing resin, 13 ... Projection part, 14 ... Sensor area | region, 15 ... Resistance element, 16 ... Position of both ends of projection part, 17 ... Positions at both ends of the sensor chip, 18 ... curved portion on the back side of the metal plate, 31 ... sensor chip mounting area, 32 ... sensor chip non-mounting area

Claims (7)

A sensor chip comprising a front surface, a plurality of piezoresistive elements formed on the front surface side, a plurality of electrode pads electrically connected to the piezoresistive elements, and a back surface located on the opposite side of the surface;
A metal plate bonded to the back surface via a bonding material;
A protrusion formed on the opposite side of the surface of the metal plate to which the sensor chip is joined, and corresponding to the back surface;
A mechanical quantity measuring device comprising: A sensor chip comprising a front surface, a plurality of piezoresistive elements formed on the front surface side, a plurality of electrode pads electrically connected to the piezoresistive elements, and a back surface located on the opposite side of the surface;
A metal plate bonded to the back surface via a bonding material;
A convex curved portion formed on the opposite side of the surface of the metal plate to which the sensor chip is joined, corresponding to the back surface;
A mechanical quantity measuring device comprising: The mechanical quantity measuring device according to claim 1, wherein the longitudinal direction of the protrusion is in a positional relationship perpendicular to the longitudinal direction of the metal plate. 3. The mechanical quantity measuring device according to claim 2, wherein both end positions of the projecting portion in the short direction are present inside positions of both end faces of the sensor chip. The mechanical quantity measuring device according to claim 1 or 2, wherein the entire back surface of the metal plate is fixed to an object to be measured with an adhesive. 3. The mechanical quantity measuring device according to claim 1, wherein screw holes are provided at both ends of the metal plate. 3. The mechanical measurement device according to claim 2, wherein the thickness of the metal plate in the curved portion is thicker than the thickness of other portions.