Strain gauge module and manufacturing method for the same

Abstract

To provide a strain gauge module that can be handled easily.SOLUTION: This strain gauge module includes: a thin substrate having a first surface and a second surface on the opposite side of the first surface, the second surface serving as a mount surface to be mounted on a measurement object; a film-shaped strain detection device mounted on the first surface, including a resistor and a terminal electrically connected to the resistor on a third surface on the opposite side of the thin substrate, and configured to detect the strain generated in the measurement object; a re-wiring substrate having a fourth surface facing the third surface and a fifth surface on the opposite side of the fourth surface, having an internal connection electrode on the fourth surface, and having an external connection electrode on the fifth surface; and a metal alloy electrode that joins the terminal and the internal connection electrode. A surface of the metal alloy electrode on the terminal side is a flat surface. The metal alloy electrode is subjected to metal diffusion junction with the terminal by a fusion conductive adhesive.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] The present invention relates to a strain gauge module and a method for manufacturing the same. [Background technology]

[0002] As a film-like device, for example, a strain gauge having a resistor formed on a substrate such as a flexible polyimide is known (see, for example, Patent Document 1). The terminals of such a film-like device and a circuit that processes the output of the film-like device are connected by, for example, an input / output cable (lead wire, etc.).

[0003] However, because the film-like device is small, it is difficult to connect input / output cables to the terminals. Also, because the film-like device is small, it is difficult to attach it to the object to be measured. Thus, the film-like device is difficult to handle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-185346 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above-mentioned points, and has an object to provide a strain gauge module that is easy to handle. [Means for solving the problem]

[0006] This strain gauge module has a thin plate substrate having a first surface and a second surface opposite to the first surface, with the second surface being an attachment surface to an object to be measured, a film-shaped strain detection device mounted on the first surface and having a resistor and a terminal electrically connected to the resistor on a third surface side opposite to the thin plate substrate, and detecting strain occurring in the object to be measured, a rewiring substrate having a fourth surface opposite to the third surface and a fifth surface opposite to the fourth surface, with an internal connection electrode provided on the fourth surface and an external connection electrode provided on the fifth surface, and a metal alloy electrode joining the terminal and the internal connection electrode, wherein the surface of the metal alloy electrode facing the terminal is a flat surface, and the metal alloy electrode is metal diffusion bonded to the terminal with a fusible conductive adhesive. Effect of the Invention

[0007] According to the disclosed technique, it is possible to provide a strain gauge module that is easy to handle. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge module according to the first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a strain gauge module according to a first embodiment. [Diagram 3] 2 is a plan view showing a state in which a rewiring substrate, a metal alloy electrode, and a covering member are removed from FIG. 1. [Figure 4] 1A to 1C are diagrams illustrating a manufacturing process of the strain gauge module. [Diagram 5] FIG. 1 is a diagram (part 1) showing the evaluation results of the strain gauge module 1X. [Figure 6] 1 is a diagram (part 1) showing the evaluation results of the strain gauge module 1. FIG. [Figure 7] FIG. 2 is a diagram (part 2) showing the evaluation results of the strain gauge module 1X. [Figure 8] FIG. 2 is a diagram (part 2) showing the evaluation results of the strain gauge module 1. [Figure 9]11 is a cross-sectional view illustrating a strain gauge module according to a second embodiment. FIG. [Figure 10] FIG. 11 is a diagram showing the evaluation results of the strain gauge module 2X. [Figure 11] FIG. 11 is a diagram showing the evaluation results of the strain gauge module 2. [Figure 12] 13 is a partial cross-sectional view illustrating a strain gauge module according to a third embodiment. FIG. [Figure 13] 13 is a partial cross-sectional view illustrating a strain gauge module according to a fourth embodiment. FIG. [Figure 14] FIG. 13 is a diagram illustrating the formation of a flat surface. [Figure 15] 13 is a plan view illustrating a strain gauge module according to a fifth embodiment. FIG. [Figure 16] 13 is a cross-sectional view illustrating a strain gauge module according to a fifth embodiment. FIG. [Figure 17] 16 is a plan view showing a state in which the rewiring substrate, the metal alloy electrode, and the covering member are removed from FIG. 15. FIG. [Figure 18] 16 is a see-through view of the rear surface side of the rewiring board of FIG. 15. [Figure 19] FIG. 2 is a diagram showing a bridge circuit. [Figure 20] FIG. 11 is a plan view (part 1) showing another example of the film-shaped strain detection device. [Figure 21] FIG. 2 is a plan view (part 2) showing another example of the film-shaped strain detection device. [Figure 22] 13 is a cross-sectional view illustrating a strain gauge module according to a sixth embodiment. FIG. [Diagram 23] 13 is a bottom view illustrating the strain gauge module according to the sixth embodiment. FIG. [Figure 24] FIG. 1 shows the evaluation results of strain gauge modules 6 and 6X (part 1). [Diagram 25] FIG. 2 is a diagram (part 2) showing the evaluation results of the strain gauge modules 6 and 6X. [Figure 26] 1 is a cross-sectional view showing an example of use of a strain gauge module 6. FIG. [Figure 27]FIG. 13 is a cross-sectional view illustrating a strain gauge module according to a modified example of the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0010] First embodiment (Strain gauge module) Fig. 1 is a plan view illustrating the strain gauge module according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge module according to the first embodiment, showing a cross section along line AA in Fig. 1. Fig. 3 is a plan view showing a state in which a rewiring substrate, a metal alloy electrode, and a covering member are removed from Fig. 1.

[0011] 1 to 3, the strain gauge module 1 includes a thin plate substrate 10, an adhesive 20, a film-shaped strain detection device 30, a rewiring substrate 40, a metal alloy electrode 50, and a covering member 61. The strain gauge module 1 is attached to an object to be measured and can detect strain occurring in the object to be measured.

[0012] The strain gauge module 1 is, for example, substantially rectangular or substantially square in plan view. The strain gauge module 1 may be substantially circular or substantially elliptical in plan view, or may be another shape. The maximum length of the strain gauge module 1 may be, for example, about 1 mm or more and 50 mm or less in plan view. The thickness of the strain gauge module 1 may be, for example, about 0.3 mm or more and 5 mm or less.

[0013] The maximum length of the strain gauge module 1 is defined as the length of the longest straight line that can be drawn continuously within the strain gauge module 1 in a plan view. For example, the maximum length of the strain gauge module 1 is the length of the diagonal when the strain gauge module 1 is rectangular or square in a plan view, the diameter when the strain gauge module 1 is circular, or the major axis when the strain gauge module 1 is elliptical.

[0014] The thin plate substrate 10 is a member on which the film-shaped strain detection device 30 is disposed. In detail, the thin plate substrate 10 has a first surface 10a and a second surface 10b opposite to the first surface 10a. In the illustrated example, the first surface 10a is the upper surface, and the second surface 10b is the lower surface. The first surface 10a is, for example, parallel to the second surface 10b. The film-shaped strain detection device 30 is mounted on the first surface 10a of the thin plate substrate 10, and the second surface 10b is a surface to be attached to the object to be measured.

[0015] Here, the thin plate substrate refers to a substrate having a thickness of 200 μm or less. The thickness of the thin plate substrate 10 is preferably 20 μm or more and 120 μm or less, more preferably 20 μm or more and 80 μm or less, and even more preferably 20 μm or more and 50 μm or less. By making the thickness of the thin plate substrate 10 20 μm or more, the strain can be stably detected. By making the thickness of the thin plate substrate 10 120 μm or less, the strain can be detected with good sensitivity. In addition, by making the thickness of the thin plate substrate 10 thinner, the strain can be detected with even better sensitivity. In addition, if the thickness of the thin plate substrate 10 is 20 μm or more and 80 μm or less, the thin plate substrate 10 can be easily fixed to a curved measurement object. If the thickness of the thin plate substrate 10 is 20 μm or more and 50 μm or less, the thin plate substrate 10 can be even more easily fixed to a curved measurement object.

[0016] The surface roughness Ra of the first surface 10a of the thin plate substrate 10 is preferably 3 μm or more and 20 μm or less, more preferably 3 μm or more and 10 μm or less, and even more preferably 3 μm or more and 5 μm or less. By setting the surface roughness Ra of the first surface 10a of the thin plate substrate 10 to 3 μm or more and 20 μm or less, it is possible to reduce the effect of the surface roughness Ra of the first surface 10a of the thin plate substrate 10 on the film-like strain detection device 30, and the strain can be easily and accurately measured. Here, the surface roughness Ra is a type of numerical value that represents the surface roughness, and is called the arithmetic mean roughness.

[0017] For example, a metal can be used as the material of the thin plate substrate 10. As the metal, SUS (stainless steel) having high hardness (easy propagation of strain) for transmitting strain is preferable, but the metal is not limited to this, and aluminum, copper alloy, etc. may be used. SUS is also preferable because it is easily available.

[0018] The thin plate substrate 10 may be made of an amorphous material or a nanocrystalline material. An example of an amorphous material is glass. An example of a nanocrystalline material is an amorphous alloy. Amorphous alloys are mainly Fe-, Ni-, or cobalt-based alloys that contain 15 to 30 atomic % of boron, carbon, silicon, phosphorus, etc., and are excellent in strength, corrosion resistance, and soft magnetic properties, and can be used in a wide range of environments.

[0019] The size of the thin plate substrate 10 is not particularly limited, but is larger than the size of the film-shaped strain detection device 30 in a plan view.

[0020] The film-shaped strain detection device 30 is mounted on the first surface 10a of the thin plate substrate 10 via an adhesive 20. For example, an epoxy resin or the like can be used as the adhesive 20. The flexural modulus of the adhesive 20 can be, for example, 3 GPa or more and 20 GPa or less. The adhesive 20 may contain a filler as necessary. When the adhesive 20 contains a filler, the filler contained may be an inorganic filler or an organic filler. When the adhesive 20 contains an inorganic filler, the filler diameter is preferably 5 μm or less, and when the adhesive 20 contains an organic filler, the filler diameter is preferably 10 μm or less.

[0021] The thickness of the adhesive 20 is preferably 30 μm or less. If the thickness of the adhesive 20 is 30 μm or less, the distortion of the thin plate substrate 10 can be efficiently transmitted to the film-shaped distortion detection device 30.

[0022] It is preferable that the entire lower surface of the film-shaped strain detection device 30 is adhered to the first surface 10a of the thin plate substrate 10 by the adhesive 20. In this case, it is preferable that the variation in thickness of the adhesive 20 is ±5 μm or less. This allows the entire film-shaped strain detection device 30 to be held flat on the first surface 10a of the thin plate substrate 10, so that the strain of the thin plate substrate 10 can be transmitted to the film-shaped strain detection device 30 more efficiently.

[0023] The film-shaped strain detection device 30 has a substrate 31, a resistor 32, wiring 33, and terminals 34a and 34b. The film-shaped strain detection device 30 detects strain occurring in a measurement object. There is no particular limit to the size of the film-shaped strain detection device 30, but from the viewpoint of miniaturizing the strain gauge module 1, it is preferable that the film-shaped strain detection device 30 is also small. For example, the substrate 31 can be in a square or rectangular shape with a side length of about 1.5 mm to 2 mm.

[0024] The substrate 31 is a member that serves as a base layer for forming the resistor 32, and the flexible substrate 31 has a third surface 31a on which the resistor 32 and the like are formed. There is no particular limit to the thickness of the substrate 31, and it can be appropriately selected depending on the purpose. The substrate 31 can be formed, for example, from an insulating resin film such as a PI (polyimide) resin.

[0025] The resistor 32 is a thin film provided on the third surface 31a side, which is the side opposite to the thin plate substrate 10. In the illustrated example, the third surface 31a is the upper surface of the base material 31. The resistor 32 is a sensing part that generates a resistance change when strained. The resistor 32 may be formed directly on the third surface 31a, or may be formed on the third surface 31a via another layer. There is no particular limit to the thickness of the resistor 32, and it can be appropriately selected depending on the purpose, and is, for example, 0.05 μm or more and 50 μm or less.

[0026] The resistor 32 has a structure in which multiple elongated portions are arranged at regular intervals with their longitudinal directions in the same direction, and the ends of adjacent elongated portions are alternately connected to form a zigzag fold as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction.

[0027] The resistor 32 can be made of, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 32 can be made of a material containing at least one of Cr and Ni. An example of a material containing Ni is Cu-Ni (copper-nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel-chromium).

[0028] The resistor 32 may be made of a Cr mixed-phase film. Here, the Cr mixed-phase film is made of Cr, CrN, Cr 2 The Cr mixed-phase film may contain unavoidable impurities such as chromium oxide. When the Cr mixed-phase film is used as the resistor 32, the film-shaped strain detection device 30 can be made highly sensitive and compact.

[0029] The terminals 34a and 34b are provided on the third surface 31a. Specifically, the terminals 34a and 34b are provided on the wiring 33 and electrically connected to the resistor 32. The terminals 34a and 34b are connected to both ends of the resistor 32 via the wiring 33 made of copper or the like, and are formed, for example, in a rectangular or circular shape in a plan view. The terminals 34a and 34b are a pair of electrodes for outputting a change in the resistance value of the resistor 32 caused by distortion. The terminals 34a and 34b are made of, for example, copper or the like. A gold film or the like may be laminated on the surface of the copper or the like.

[0030] The rewiring substrate 40 is disposed above the first surface 10a of the thin plate substrate 10, sandwiching the film-shaped strain detection device 30. The rewiring substrate 40 has a base material 41, internal connection electrodes 42a and 42b, external connection electrodes 43a and 43b, and a through wiring 44.

[0031] The base material 41 of the rewiring board 40 has a fourth surface 41a facing the third surface 31a of the film-shaped strain detection device 30, and a fifth surface 41b opposite to the fourth surface 41a. In the illustrated example, the fourth surface 41a is the lower surface, and the fifth surface 41b is the upper surface. Examples of materials for the base material 41 include resin, ceramic, silicon, and the like. The base material 41 may be, for example, a reinforcing material such as glass cloth impregnated with a resin such as an epoxy resin.

[0032] The distance between the fourth surface 41a of the rewiring substrate 40 and the third surface 31a of the film-shaped strain detection device 30 can be, for example, 100 μm or more and 200 μm or less. If the distance between the fourth surface 41a and the third surface 31a is 100 μm or more, the film-shaped strain detection device 30 is less susceptible to the effects of thermal expansion of the rewiring substrate 40, thereby reducing the risk of deterioration of the characteristics (sensitivity) of the film-shaped strain detection device 30. If the distance between the fourth surface 41a and the third surface 31a is 200 μm or less, the strain gauge module 1 can be made low-profile.

[0033] The internal connection electrodes 42a and 42b are provided on the fourth surface 41a, and the external connection electrodes 43a and 43b are provided on the fifth surface 41b. The metal alloy electrode 50 joins the terminal 34a of the film-shaped strain detection device 30 to the internal connection electrode 42a. The metal alloy electrode 50 also joins the terminal 34b of the film-shaped strain detection device 30 to the internal connection electrode 42b.

[0034] The external connection electrode 43a is electrically connected to the internal connection electrode 42a via a through-wire 44 that penetrates the base material 41. The external connection electrode 43b is electrically connected to the internal connection electrode 42b via a through-wire 44 that penetrates the base material 41. That is, the external connection electrodes 43a and 43b are electrically connected to the terminals 34a and 34b, and a change in the resistance value of the resistor 32 caused by distortion can be output to the outside. The external connection electrode 43a may be electrically connected to the internal connection electrode 42a via the through-wire 44 and a wire provided on the rewiring substrate 40. The same applies to the external connection electrode 43b.

[0035] The internal connection electrodes 42a and 42b, the external connection electrodes 43a and 43b, and the through wiring 44 may be made of, for example, copper. A gold film or the like may be laminated on the surfaces of the external connection electrodes 43a and 43b. The metal alloy electrode 50 may be made of, for example, tin-silver-copper. The melting point of tin-silver-copper is about 220°C.

[0036] The covering member 61 is filled in the area where the first surface 10a and the third surface 31a face the fourth surface 41a to cover the film-shaped strain detection device 30 and the metal alloy electrode 50, and also covers the side surface of the rewiring substrate 40. In other words, the covering member 61 serves both as an underfill resin that protects the film-shaped strain detection device 30 and as an exterior. The side surface of the rewiring substrate 40 is a surface that connects the outer edge of the fourth surface 41a and the outer edge of the fifth surface 41b. The side surface of the rewiring substrate 40 is, for example, perpendicular to the first surface 10a. The perpendicular here includes a range of 90±5 degrees.

[0037] The covering member 61 can be formed, for example, from a thermosetting resin containing a filler 70. Examples of the thermosetting resin include an epoxy resin or a phenol resin. By providing the covering member 61, it is possible to improve the humidity resistance and temperature resistance. In addition, since the filler 70 distributes stress and suppresses the cure shrinkage of the thermosetting resin, unnecessary stress is not applied to the film-shaped strain detection device 30, and the effect on the characteristics (sensitivity) of the film-shaped strain detection device 30 can be reduced.

[0038] The filler 70 is, for example, an oxide-based filler. Examples of the oxide-based filler include fillers such as silicon dioxide and alumina. The filler 70 is preferably spherical. If the filler 70 is spherical, the effect of suppressing the curing shrinkage of the thermosetting resin is increased. In the present application, the spherical shape is not limited to an exact sphere, and includes a shape in which the difference between the long and short diameters that are perpendicular to each other is within a range of 10%.

[0039] The particle size distribution of the filler 70 is preferably such that the maximum diameter is, for example, 50 μm. If the maximum particle size of the filler 70 is 50 μm, the covering member 61 can be sufficiently filled even if the gap between the third surface 31a and the fourth surface 41a is about 100 μm.

[0040] The content of the filler 70 is preferably 50% or more and 80% or less of the equivalent weight of the covering member 61. If the content of the filler 70 is 50% or more of the equivalent weight of the covering member 61, the effect of suppressing the cure shrinkage of the thermosetting resin can be sufficiently exhibited. If the content of the filler 70 is 80% or less of the equivalent weight of the covering member 61, the covering member 61 can be sufficiently filled even if the gap between the third surface 31a and the fourth surface 41a is about 100 μm.

[0041] In this manner, in the strain gauge module 1, the rewiring substrate 40 is disposed on the film-shaped strain detection device 30, and the rewiring substrate 40 is provided with external connection electrodes 43a and 43b that are electrically connected to the terminals 34a and 34b of the film-shaped strain detection device 30. This improves the degree of freedom in the size and arrangement of the external connection electrodes 43a and 43b, thereby realizing a strain gauge module 1 that is easy to handle.

[0042] For example, while the size of the terminals 34a and 34b is extremely small (about 250 μm to 500 μm), the size of the external connection electrodes 43a and 43b can be about 1500 μm to 2000 μm. Therefore, input / output cables and the like can be easily connected to the external connection electrodes 43a and 43b.

[0043] Furthermore, when connecting input / output cables to the terminals 34a and 34b, the wire diameter must be extremely thin, which reduces resistance to disturbance noise. In contrast, cables with a larger wire diameter can be connected to the external connection electrodes 43a and 43b, which improves resistance to disturbance noise.

[0044] In addition, since the strain gauge module 1 is packaged, it can be easily attached to an object to be measured. In addition, since the strain gauge module 1 is packaged, it can be used with automatic inspection equipment and can be mounted by automatic machines, and the packaging format for transportation in the manufacturing process can be the same as that for ordinary semiconductor devices.

[0045] Moreover, in the strain gauge module 1, a module structure with excellent environmental resistance can be realized by providing the covering member 61 containing the filler 70. This reduces the characteristic fluctuation of the film-shaped strain detection device 30, enabling highly sensitive and stable strain detection.

[0046] In addition, since the bottom layer of the strain gauge module 1 is the thin plate substrate 10, the second surface 10b of the thin plate substrate 10 can be easily fixed to the measurement object using a liquid or film (tape) adhesive or pressure-sensitive adhesive. The thickness of the adhesive or pressure-sensitive adhesive can be, for example, about 25 μm.

[0047] That is, the strain gauge module 1 is easy to attach to the measurement object because the bottom layer is not made of flexible resin (polyimide, etc.) as in conventional strain gauges. Also, since polyimide is a poorly adhesive material, a special adhesion method (heating and pressure) is required to attach it to the measurement object, but no special adhesion method is required to attach the thin plate substrate 10 to the measurement object.

[0048] In the first embodiment, the film-shaped strain detection device may have a plurality of resistors. For example, the film-shaped strain detection device may have a structure having two resistors, or a structure having four resistors as in the fifth embodiment. The rewiring substrate 40 may have a multi-layer wiring structure, and in this case, the internal connection electrode may be electrically connected to the external connection electrode via the multi-layer wiring structure.

[0049] (Manufacturing method of strain gauge module) Fig. 4 is a diagram for explaining the manufacturing process of the strain gauge module. As shown in Fig. 4, in order to manufacture the strain gauge module 1, first, a process of preparing a thin plate substrate is executed as step S1. Specifically, a thin plate substrate 10 is prepared, which has a first surface 10a and a second surface 10b opposite to the first surface 10a, and the second surface 10b is used as a mounting surface for a measurement object.

[0050] Next, in step S2, a process of mounting the film-shaped strain detection device 30 is performed. Specifically, the film-shaped strain detection device 30 is prepared, which includes a resistor 32 and terminals 34a and 34b electrically connected to the resistor 32 on the third surface 31a side and detects strain occurring in the measurement object. Then, the film-shaped strain detection device 30 is mounted on the first surface 10a via the adhesive 20 so that the third surface 31a is on the opposite side to the thin plate substrate 10.

[0051] Next, in step S3, a bonding process is performed. Specifically, a rewiring substrate 40 is prepared, the rewiring substrate 40 having a fourth surface 41a and a fifth surface 41b opposite to the fourth surface 41a, with internal connection electrodes 42a and 42b provided on the fourth surface 41a and external connection electrodes 43a and 43b provided on the fifth surface 41b. The fourth surface 41a is then disposed to face the third surface 31a, and the terminals 34a and 34b are bonded to the internal connection electrodes 42a and 42b via the metal alloy electrodes 50.

[0052] Specifically, first, a metal alloy electrode 50 is formed on each of the internal connection electrodes 42a and 42b. For example, a predetermined amount of metal alloy paste is placed on each of the internal connection electrodes 42a and 42b, and the metal alloy paste is melted and formed into a dome shape by liquid phase surface tension, and then solidified to form the metal alloy electrode 50. Next, the rewiring substrate 40 is arranged so that the metal alloy electrode 50 contacts the terminals 34a and 34b, and the metal alloy electrode 50 is melted again and solidified, thereby joining the terminals 34a and 34b and the internal connection electrodes 42a and 42b via the metal alloy electrode 50.

[0053] Next, in step S4, a process of forming the covering member 61 is performed. Specifically, the covering member 61 is filled in the area where the first surface 10a, the third surface 31a, and the fourth surface 41a face each other to cover the film-shaped strain detection device 30 and the metal alloy electrode 50, and also covers the side surface of the rewiring substrate 40. The covering member 61 can be formed, for example, by a compression molding method. The pressure when filling the covering member 61 can be, for example, about 0.2 MPa. The covering member 61 may be formed by a transfer molding method, an injection molding method, or the like. Thereafter, the rewiring substrate 40, etc. is cut vertically using a dicing device or the like, as necessary, to separate into a plurality of strain gauge modules 1. In the rewiring substrate 40 after cutting, a side surface with good surface accuracy is obtained. Through the above process, the strain gauge module 1 is completed.

[0054] (Strain gauge module evaluation) [Rating 1] The strain gauge module was subjected to a stepwise change in humidity to evaluate the change over time in the output of the strain gauge module. The evaluation was performed on two samples each of the strain gauge module 1X, which is configured by removing the covering member 61 from the strain gauge module 1, and the strain gauge module 1. The output was measured by connecting the external connection electrodes 43a and 43b to a Wheatstone bridge circuit.

[0055] FIG. 5 is a diagram (part 1) showing the evaluation results of the strain gauge module 1X. FIG. 6 is a diagram (part 1) showing the evaluation results of the strain gauge module 1. In FIGS. 5 and 6, the bold stepped waveform indicates the change in humidity, and the thin line indicates the change in output. As shown in FIG. 5, the strain gauge module 1X, which does not have a covering member 61, changes its output voltage over time due to the influence of humidity. In contrast, as shown in FIG. 6, the strain gauge module 1, which has a covering member 61, hardly shows any change in output voltage due to the influence of humidity. Note that in FIG. 6, the output changes of the two samples are almost the same, so the output changes appear as a single line.

[0056] [Rating 2] The strain gauge module was subjected to an intermittent low-frequency vibration of 25 Hz, and the change in resistance value over time of the strain gauge module was evaluated. The evaluation was performed on four samples each of the strain gauge module 1X, which was configured by removing the covering member 61 from the strain gauge module 1, and the strain gauge module 1. The resistance value was calculated by taking the output power under strain load as the combined resistance.

[0057] FIG. 7 is a diagram (part 2) showing the evaluation results of the strain gauge module 1X. FIG. 8 is a diagram (part 2) showing the evaluation results of the strain gauge module 1. As shown in FIG. 7, the resistance value of the strain gauge module 1X that does not have the covering member 61 tends to change in the same direction when the number of times that low-frequency vibration is applied increases to a certain extent. In contrast, as shown in FIG. 8, the resistance value of the strain gauge module 1 that has the covering member 61 hardly changes from the initial value even when the number of times that low-frequency vibration is applied increases.

[0058] [Evaluation Results] As shown in evaluations 1 and 2, by providing the covering member 61 containing the filler 70, it is possible to improve the environmental resistance compared to the case where the covering member 61 containing the filler 70 is not provided. This reduces the characteristic fluctuation of the film-shaped strain detection device 30, and enables highly sensitive strain detection with excellent stability.

[0059] Second Embodiment In the second embodiment, an example will be described in which a covering member different from that in the first embodiment is used. Note that in the second embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0060] Fig. 9 is a cross-sectional view illustrating the strain gauge module according to the second embodiment, and shows a cross section corresponding to Fig. 2. Note that the plan views shown in Figs. 1 and 3 are the same for the strain gauge module according to the second embodiment as for the strain gauge module according to the first embodiment.

[0061] 9, the strain gauge module 2 differs from the strain gauge module 1 in that the covering member 61 is replaced with a covering member 62.

[0062] The covering member 62 is a thermosetting resin. Specifically, the covering member 62 is formed from a gel or a resin with a long chain structure. By forming the covering member 62 from a gel or a resin with a long chain structure, it is possible to avoid shrinkage that occurs as a result of a hardening reaction of a typical resin. This prevents unnecessary stress from being applied to the film-shaped strain detection device 30, and the effect on the characteristics (sensitivity) of the film-shaped strain detection device 30 can be significantly reduced.

[0063] The covering member 62 can be formed from, for example, silicone gel or silicone resin with a long chain structure. For the covering member 62, a material having a modified silicone group, such as modified silicone epoxy, can also be used. Silicone rubber is not preferable as a material for the covering member 62 because it causes a thermal contraction reaction. The covering member 62 does not contain a solvent or a filler. By not containing a solvent, adverse effects on the film-shaped strain detection device 30 can be prevented. Furthermore, in the covering member 62, the long chains are entangled with each other to act as a cushion and relieve stress, so there is no need to contain a filler.

[0064] The hardness of the covering member 62 is, for example, A30 (JIS K6253, ASTM-D2240, ISO-48(1-6)). The hardness of the covering member 62 is preferably A hardness or more and D hardness or less. When the hardness is in this range, the effect of covering with the covering member 62 on the characteristics (sensitivity) of the film-shaped strain detection device 30 can be reduced.

[0065] In the second embodiment, the film-shaped strain detection device may have a plurality of resistors. For example, the film-shaped strain detection device may have a structure having two resistors, or a structure having four resistors as in the fifth embodiment. The rewiring substrate 40 may have a multi-layer wiring structure, and in this case, the internal connection electrode may be electrically connected to the external connection electrode via the multi-layer wiring structure.

[0066] 4, in step S4, the covering member 62 is formed from gel or a resin with a long chain structure. The covering member 62 can be formed by using, for example, a compression molding method. The covering member 62 may also be formed by using a transfer molding method, an injection molding method, or the like. Through the above steps, the strain gauge module 2 is completed.

[0067] (Strain gauge module evaluation) [Rating 3] The strain gauge module was stored in a high-temperature and high-humidity environment of 85°C and 85% RH, and the output of the strain gauge module was evaluated for change over time. The evaluation was performed on four samples each of the strain gauge module 2X, which was configured by removing the covering member 62 from the strain gauge module 2, and the strain gauge module 2. The output was measured by connecting the external connection electrodes 43a and 43b to a Wheatstone bridge circuit.

[0068] Fig. 10 is a diagram showing the evaluation results of the strain gauge module 2X. Fig. 11 is a diagram showing the evaluation results of the strain gauge module 2. As shown in Fig. 10, the strain gauge module 2X, which does not have a covering member 62, is affected by temperature and / or humidity, and the amount of output fluctuation changes significantly over time. In contrast, as shown in Fig. 11, the strain gauge module 2, which has a covering member 62, is able to significantly reduce output fluctuations caused by the effects of temperature and / or humidity.

[0069] [Evaluation Results] As shown in Evaluation 3, the strain gauge module 2 can realize a module structure with excellent environmental resistance by providing the covering member 62. This reduces the characteristic fluctuation of the film-shaped strain detection device 30, enabling stable and highly sensitive strain detection.

[0070] Third embodiment The third embodiment shows an example in which the joining form of the metal alloy electrodes is different from that of the first embodiment etc. In the third embodiment, the description of the same components as those of the embodiments already described may be omitted.

[0071] Fig. 12 is a partial cross-sectional view illustrating a strain gauge module according to a third embodiment, showing a part of the cross section corresponding to Fig. 2. Note that the plan views shown in Figs. 1 and 3 are the same for the strain gauge module according to the third embodiment as for the strain gauge module according to the first embodiment.

[0072] 12, in the strain gauge module 3, the metal alloy electrode 50 is metal diffusion bonded to the terminal 34a by the fusible conductive adhesive 51. The same is true for the terminal 34b (not shown). The metal alloy electrode 50 is non-meltable at the melting temperature of the fusible conductive adhesive 51. In other words, the fusible conductive adhesive 51 has a lower melting point than the metal alloy electrode 50.

[0073] The meltable conductive adhesive 51 contains, for example, metal powder, and the metal alloy electrode 50 is metal diffusion bonded to the terminal 34a via the metal powder. The same applies to the bonding between the metal alloy electrode 50 and the terminal 34b. The metal powder is, for example, spherical. The spherical metal powder contains, for example, bismuth and tin. The spherical metal powder has, for example, a melting temperature of about 140°C. The particle size distribution of the spherical metal powder is, for example, a diameter of 25 μm or more and 45 μm or less. The particle size distribution of the spherical metal powder may be a diameter of 20 μm or more and 38 μm or less, or a diameter of 15 μm or more and 25 μm or less.

[0074] The strain gauge module 3 preferably has an insulating resin 52 that covers the side surface of the metal alloy electrode 50, contacts the terminals 34a and 34b, and bonds the metal alloy electrode 50 to the terminals 34a and 34b. This can improve the bonding strength between the metal alloy electrode 50 and the terminals 34a and 34b.

[0075] 4, in step S3, the metal alloy electrodes 50 are formed on the internal connection electrodes 42a and 42b. For example, a predetermined amount of metal alloy paste is placed on each of the internal connection electrodes 42a and 42b, and the metal alloy paste is melted and formed into a dome shape by liquid phase surface tension, and then solidified to form the metal alloy electrodes 50.

[0076] Next, prepare the fusible conductive adhesive 51. For example, prepare the fusible conductive adhesive 51 containing spherical metal powder, insulating resin such as epoxy resin, and organic acid. Then, the prepared fusible conductive adhesive 51 is placed on the terminals 34a and 34b.

[0077] Next, the rewiring substrate 40 is placed on the film-shaped strain detection device 30 so that the fusible conductive adhesive 51 and the metal alloy electrode 50 are in contact with each other. Then, the fusible conductive adhesive 51 is heated to metal diffusion bond the metal alloy electrode 50 to the terminals 34a and 34b with the fusible conductive adhesive 51. At this time, the heating is performed at a temperature at which the fusible conductive adhesive 51 melts but the metal alloy electrode 50 does not melt. This makes it possible to prevent the metal alloy electrode 50 from being deformed.

[0078] By heating, the metal alloy electrode 50 is metal diffusion bonded to the terminals 34a and 34b via the metal powder contained in the fusible conductive adhesive 51. At the same time, the insulating resin contained in the fusible conductive adhesive 51 flows out along the side surfaces of the metal alloy electrode 50, forming insulating resin 52 that covers the side surfaces of the metal alloy electrode 50 and comes into contact with the terminals 34a and 34b to bond the metal alloy electrode 50 to the terminals 34a and 34b. Thereafter, the strain gauge module 3 is completed by executing step S4 in FIG.

[0079] Thus, in the strain gauge module 3, the metal alloy electrode 50 is metal diffusion bonded to the terminals 34a and 34b by the fusible conductive adhesive 51. Since the metal alloy electrode 50 does not melt when heated for metal diffusion bonding, a gap equal to or greater than the height of the metal alloy electrode 50 can be secured between the film-shaped strain detection device 30 and the rewiring substrate 40. Furthermore, the metal alloy electrode 50 can be connected to the terminals 34a and 34b with low resistance by the metal diffusion bonding.

[0080] For example, if a silver paste or solder paste with a melting point similar to that of the metal alloy electrode 50 is used instead of the fusible conductive adhesive 51 with a lower melting point than the metal alloy electrode 50, when the rewiring substrate 40 is placed on the film-shaped strain detection device 30, the silver paste or solder paste melts and the metal alloy electrode 50 also melts. As a result, the distance between the film-shaped strain detection device 30 and the rewiring substrate 40 may not be constant, which may adversely affect the strain detection characteristics. The strain gauge module 3 can prevent such problems from occurring.

[0081] In the third embodiment, the covering member can be provided as necessary. In addition, when the covering member is provided, the covering member 61 or the covering member 62 may be used. In the third embodiment, the film-shaped strain detection device may have a plurality of resistors. For example, the film-shaped strain detection device may have a structure having two resistors, or a structure having four resistors as in the fifth embodiment. In addition, the rewiring substrate 40 may have a multilayer wiring structure, and in this case, the internal connection electrode may be electrically connected to the external connection electrode via the multilayer wiring structure.

[0082] Fourth embodiment In the fourth embodiment, an example in which the shape of the joining surface of the metal alloy electrode is different from that in the third embodiment is shown. Note that in the fourth embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0083] Fig. 13 is a partial cross-sectional view illustrating a strain gauge module according to a fourth embodiment, showing a part of the cross section corresponding to Fig. 2. Note that the plan views shown in Figs. 1 and 3 are the same for the strain gauge module according to the first embodiment as for the strain gauge module according to the fourth embodiment.

[0084] 13, the strain gauge module 4 uses a metal alloy electrode 50A to join the terminal 34a and the internal connection electrode 42a. Similarly, the metal alloy electrode 50A is used to join the terminal 34b and the internal connection electrode 42b. The metal alloy electrode 50A differs from the metal alloy electrode 50 in that the surface on the terminals 34a and 34b side of the film-shaped strain detection device 30 is a flat surface 55. The surface roughness Ra of the flat surface 55 is preferably 5 μm or more and 200 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0085] To form the metal alloy electrode 50A, as described in step S3 of Fig. 4, a predetermined amount of metal alloy paste is placed on each of the internal connection electrodes 42a and 42b, and the metal alloy paste is melted and then solidified to form a dome-shaped metal alloy electrode 50 as shown in the upper arrow of Fig. 14. Thereafter, the top side of the metal alloy electrode 50 is polished by a predetermined amount to form a flat surface 55 on the side opposite the internal connection electrodes 42a and 42b as shown in the lower arrow of Fig. 14, to form the metal alloy electrode 50A. Note that the internal connection electrodes 42a and 42b are not shown in Fig. 14.

[0086] The polishing can be performed by, for example, a mechanical method or a mechanochemical method. Specifically, the polishing can be performed by, for example, using a back grinder. The variation in height of each metal alloy electrode 50A after polishing can be set to 3 μm or less. In other words, the difference in height between the highest metal alloy electrode 50A and the lowest metal alloy electrode 50A can be set to 3 μm or less.

[0087] After forming the flat surface 55, the metal alloy electrode 50A is metal diffusion bonded to the terminals 34a and 34b via the metal powder contained in the fusible conductive adhesive 51 in the same manner as in the third embodiment. At the same time, the insulating resin contained in the fusible conductive adhesive 51 flows out along the side surfaces of the metal alloy electrode 50A, covering the side surfaces of the metal alloy electrode 50A and contacting the terminals 34a and 34b to form the insulating resin 52 that bonds the metal alloy electrode 50A to the terminals 34a and 34b.

[0088] Since the metal alloy electrode 50A does not melt when heated to perform metal diffusion bonding, the gap between the film-shaped strain detection device 30 and the rewiring substrate 40 does not shift. The fusible conductive adhesive 51 located between the flat surface 55 and the terminals 34a and 34b is extremely thin, so it has little effect on the gap between the film-shaped strain detection device 30 and the rewiring substrate 40. After performing metal diffusion bonding, the strain gauge module 4 is completed by performing step S4 in FIG.

[0089] In this manner, by using the metal alloy electrode 50A having the flat surface 55, the distance between the film-shaped strain detection device 30 and the rewiring substrate 40 can be made substantially constant. This makes the thickness of the covering member 61 filled between the film-shaped strain detection device 30 and the rewiring substrate 40 substantially uniform, enabling good strain sensing.

[0090] In order to make the height of the metal alloy electrodes 50 uniform before polishing, it is necessary to control the supply amount of the metal alloy paste that will become each metal alloy electrode 50, but it is difficult to precisely control the supply amount of the metal alloy paste. There is also a method of making the height of each metal alloy electrode uniform by using metal balls or metal posts instead of the metal alloy electrodes 50, but since metal balls and metal posts are expensive, it is not easy to adopt these methods.

[0091] According to the method using the metal alloy electrode 50A having the flat surface 55, the distance between the film-shaped strain detection device 30 and the rewiring substrate 40 can be made substantially constant in a simple manner without using expensive materials. That is, the metal alloy electrode 50A functions as an electrode for electrical connection and also functions as a spacer. By using the metal alloy electrode 50A, for example, the distance between the film-shaped strain detection device 30 and the rewiring substrate 40 can vary by 3 μm or less from a predetermined value in the range of 100 μm to 200 μm.

[0092] In the fourth embodiment, the covering member can be provided as necessary. In addition, when the covering member is provided, the covering member 61 or the covering member 62 may be used. In the fourth embodiment, the film-shaped strain detection device may have a plurality of resistors. For example, the film-shaped strain detection device may have a structure having two resistors, or a structure having four resistors as in the fifth embodiment. In addition, the rewiring substrate 40 may have a multilayer wiring structure, and in this case, the internal connection electrode may be electrically connected to the external connection electrode via the multilayer wiring structure.

[0093] Fifth embodiment In the fifth embodiment, an example in which the film-shaped strain detection device has four resistors will be described. Note that in the fifth embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0094] Fig. 15 is a plan view illustrating a strain gauge module according to a fifth embodiment. Fig. 16 is a cross-sectional view illustrating a strain gauge module according to the fifth embodiment, showing a cross section along line BB in Fig. 15. Fig. 17 is a plan view showing a state in which the rewiring substrate, the metal alloy electrode, and the covering member have been removed from Fig. 15. Fig. 18 is a see-through view of the back side of the rewiring substrate in Fig. 15.

[0095] 15 to 18, the strain gauge module 5 includes a thin plate substrate 10, an adhesive 20, a film-shaped strain detection device 30A, a rewiring substrate 40A, a metal alloy electrode 50, and a covering member 61. As shown in FIG.

[0096] The film-shaped strain detection device 30A includes, on the third surface 31a side, four resistors 32a, 32b, 32c, and 32d connected in series, and four terminals 34c, 34d, 34e, and 34f provided at the connection points of the resistors.

[0097] Each of the resistors 32a, 32b, 32c, and 32d may have, for example, the same shape as the resistor 32 and may be made of the same material as the resistor 32. The resistors 32a and 32c have, for example, the same grid direction. The resistors 32b and 32d have, for example, the same grid direction. The resistors 32a and 32c have, for example, the grid directions perpendicular to those of the resistors 32b and 32d.

[0098] One end of resistor 32a and one end of resistor 32b are connected by wiring 33, and a terminal 34d is provided at the connection point. The other end of resistor 32a and one end of resistor 32d are connected by wiring 33, and a terminal 34c is provided at the connection point. The other end of resistor 32b and one end of resistor 32c are connected by wiring 33, and a terminal 34e is provided at the connection point. The other end of resistor 32c and the other end of resistor 32d are connected by wiring 33, and a terminal 34f is provided at the connection point.

[0099] The terminals 34c, 34d, 34e, and 34f can be formed of, for example, the same material as the terminals 34a and 34b. In the illustrated example, the terminals 34c, 34d, 34e, and 34f are circular in plan view, but may be rectangular in plan view, etc.

[0100] Internal connection electrodes 42c, 42d, 42e, and 42f are provided on the fourth surface 41a of the rewiring substrate 40A. Wiring 45 is provided on the fourth surface 41a of the rewiring substrate 40A. External connection electrodes 43c, 43d, 43e, and 43f are provided on the fifth surface 41b of the rewiring substrate 40A. Wiring 46 is provided on the fifth surface 41b of the rewiring substrate 40A.

[0101] The terminal 34c is joined to the internal connection electrode 42c via a metal alloy electrode 50. The internal connection electrode 42c is electrically connected to the external connection electrode 43c via a through-wire 44. The terminal 34d is joined to the internal connection electrode 42d via a metal alloy electrode 50. The internal connection electrode 42d is electrically connected to the external connection electrode 43d via a wire 45 and a through-wire 44.

[0102] The terminal 34e is joined to the internal connection electrode 42e via a metal alloy electrode 50. The internal connection electrode 42e is electrically connected to the external connection electrode 43e via a wiring 45 and a through wiring 44. The terminal 34f is joined to the internal connection electrode 42f via a metal alloy electrode 50. The internal connection electrode 42f is electrically connected to the external connection electrode 43f via the wiring 45 and the through wiring 44.

[0103] In this manner, the resistors 32a, 32b, 32c, and 32d configure the full bridge circuit shown in Fig. 19. In the bridge circuit shown in Fig. 19, the resistor 32a is connected to the upper left side, the resistor 32b is connected to the upper right side, the resistor 32c is connected to the lower right side, and the resistor 32d is connected to the lower left side.

[0104] In the bridge circuit shown in Fig. 19, a DC voltage E is supplied from outside the strain gauge module 5 between the external connection electrode 43c, which is the connection point between the upper left side and the lower left side, and the external connection electrode 43e, which is the connection point between the upper right side and the lower right side. As a result, an analog output voltage e is generated between the external connection electrode 43d, which is the connection point between the upper left side and the upper right side, and the external connection electrode 43f, which is the connection point between the lower left side and the lower right side.0 That is, the strain of the strain gauge module 5 attached to the strain generating body can be output as an output voltage e 0 It can be detected as:

[0105] 20 is a plan view (part 1) showing another example of a film-shaped strain detection device. In the strain gauge module 5, a film-shaped strain detection device 30B shown in FIG. 20 may be used instead of the film-shaped strain detection device 30A shown in FIG.

[0106] The film-shaped strain detection device 30B includes, on the third surface 31a side, four resistors 32a, 32b, 32c, and 32d that are independent of one another, and a pair of terminals electrically connected to both ends of each resistor.

[0107] One end of resistor 32a is connected to terminal 34g via wiring 33, and the other end is connected to terminal 34h via wiring 33. One end of resistor 32b is connected to terminal 34i via wiring 33, and the other end is connected to terminal 34j via wiring 33. One end of resistor 32c is connected to terminal 34k via wiring 33, and the other end is connected to terminal 34m via wiring 33. One end of resistor 32d is connected to terminal 34n via wiring 33, and the other end is connected to terminal 34p via wiring 33.

[0108] The terminals 34g to 34p can be made of, for example, the same material as the terminals 34a and 34b. In the illustrated example, the terminals 34g to 34p are rectangular in plan view, but may be circular in plan view, for example.

[0109] The terminals 34g-34p are independent of each other within the third surface 31a, and are joined to the internal connection electrodes provided directly above the terminals 34g-34p on the fourth surface 41a of the rewiring substrate 40A via the metal alloy electrodes 50. Each of the internal connection electrodes is electrically connected to the external connection electrodes 43c-43f via a through-wire or the like. Specifically, the internal connection electrodes are connected to each other within the rewiring substrate 40A so that the four resistors 32a, 32b, 32c, and 32d are connected in series. The rewiring substrate 40A may have a multilayer wiring structure, in which case each of the internal connection electrodes is electrically connected to the external connection electrodes 43c-43f via the multilayer wiring structure.

[0110] As a result, the resistors 32a, 32b, 32c, and 32d can configure the full bridge circuit shown in Fig. 19. That is, the resistors 32a, 32b, 32c, and 32d are independent of one another within the film-shaped strain detection device 30B, but can be electrically connected by wiring within the rewiring board 40A to configure the full bridge circuit shown in Fig. 19.

[0111] 21 is a plan view (part 2) showing another example of a film-shaped strain detection device. In the strain gauge module 5, a film-shaped strain detection device 30C shown in FIG. 21 may be used instead of the film-shaped strain detection device 30A shown in FIG.

[0112] In the film-shaped strain detection device 30C, the electrical connections between the four resistors 32a, 32b, 32c, and 32d and a pair of terminals electrically connected to both ends of each resistor are similar to those of the film-shaped strain detection device 30B, but the arrangement of the resistors and terminals is different.

[0113] Even when the resistors and terminals are arranged as shown in FIG. 21, by providing internal connection electrodes directly above the terminals 34g to 34p on the fourth surface 41a of the rewiring substrate 40A and changing the routing of the wiring in the rewiring substrate 40A, the resistors 32a, 32b, 32c, and 32d can form a full bridge circuit as shown in FIG. 19.

[0114] That is, even if mutually independent resistors are arranged in various positions within the film-shaped strain detection device as in the film-shaped strain detection devices 30B and 30C, a desired circuit can be configured by changing the wiring layout in the rewiring board 40A. Also, since the resistors are independent from each other within the film-shaped strain detection device, it is possible to accommodate a wide variety of wiring connections not limited to full-bridge circuits simply by changing the rewiring board.

[0115] In addition, when resistors independent of each other are arranged in the film-shaped strain detection device as in the film-shaped strain detection devices 30B and 30C, the degree of freedom in arranging the resistors can be improved. Also, since the wiring in the film-shaped strain detection device can be reduced, the film-shaped strain detection device can be made smaller.

[0116] In the fifth embodiment, a covering member can be provided as necessary. In addition, when a covering member is provided, covering member 61 or covering member 62 may be used. In the fifth embodiment, the metal alloy electrodes may be bonded in the manner shown in the third and fourth embodiments.

[0117] Sixth embodiment In the sixth embodiment, an example in which the covering member covers different parts will be described. Note that in the sixth embodiment, the description of the same components as those in the embodiments already described may be omitted.

[0118] Fig. 22 is a cross-sectional view illustrating the strain gauge module according to the sixth embodiment, and shows a cross section corresponding to Fig. 2. Fig. 23 is a bottom view illustrating the strain gauge module according to the sixth embodiment. Note that the plan views shown in Figs. 1 and 3 are the same for the strain gauge module according to the first embodiment as for the strain gauge module according to the sixth embodiment.

[0119] 22 and 23, the strain gauge module 6 differs from the strain gauge module 1 and the like in that a covering member 61 covers the side surface of the thin plate substrate 10.

[0120] When viewed from a direction perpendicular to the second surface 10b of the thin plate substrate 10, the covering member 61 has, for example, an annular sixth surface 61a surrounding the second surface 10b. The sixth surface 61a is located, for example, on the same plane as the second surface 10b. The width W of the sixth surface 61a can be, for example, about 50 μm or more and 150 μm or less. By covering the side surface of the thin plate substrate 10 with the covering member 61, the rigidity of the entire strain gauge module 6 can be increased.

[0121] (Strain gauge module evaluation) [Rating 4] A simulation was performed on the distribution of stress when the strain gauge module was applied to the strain gauge module 6. The simulation was performed on the strain gauge module 6X in which the covering member 61 did not cover any of the side surfaces of the thin plate substrate 10, and on the strain gauge module 6.

[0122] FIG. 24 is a diagram (part 1) showing the evaluation results of the strain gauge modules 6 and 6X, and shows the simulation results of the stress distribution when a force is applied to the strain gauge module from the outer periphery side. As shown in FIG. 24, in the strain gauge module 6X, the stress is concentrated on the outer periphery of the second surface 10b. In contrast, in the strain gauge module 6, the stress changes in a stepped manner from the outer periphery of the second surface 10b toward the center. In this way, by the covering member 61 covering the side surface of the thin plate substrate 10, the propagating strain stress can be prevented from concentrating at a specific location such as an interface, and the strain can be propagated in a stepped manner.

[0123] [Rating 5] The strain gauge module was subjected to an intermittent low-frequency vibration of 25 Hz, and the change in resistance value over time of the strain gauge module was evaluated. The evaluation was performed on four samples each of the strain gauge module 6X in which the covering member 61 did not cover any of the side surfaces of the thin plate substrate 10, and the strain gauge module 6. The resistance value was recorded as the combined resistance of the output power when strain was applied.

[0124] Fig. 25 is a diagram (part 2) showing the evaluation results of the strain gauge modules 6 and 6X. The dashed line shows the evaluation result of the strain gauge module 6, and the solid line shows the evaluation result of the strain gauge module 6X. As shown in Fig. 25, the strain gauge module 6X (solid line), in which the covering member 61 does not cover the side surface of the thin plate substrate 10 at all, has a tendency for the resistance value to change in the same direction when the number of times of applying a load of low-frequency vibration increases to a certain extent. In contrast, the strain gauge module 6 (dashed line), in which the covering member 61 covers the side surface of the thin plate substrate 10, has almost no change in the rate of change in the resistance value even when the number of times of applying a load of low-frequency vibration increases.

[0125] [Evaluation Results] As shown in evaluations 4 and 5, by covering the side surface of the thin plate substrate 10 with the covering member 61, stress concentration is alleviated and environmental resistance is improved compared to the case where the covering member 61 does not cover the side surface of the thin plate substrate 10 at all. This reduces the characteristic fluctuation of the film-shaped strain detection device 30, enabling highly sensitive strain detection with excellent stability.

[0126] FIG. 26 is a cross-sectional view showing an example of use of the strain gauge module 6. As shown in FIG. 26, the strain gauge module 6 is bonded to the upper surface 120a of the measurement object 120 by, for example, an adhesive 110. For example, when the side surface of the thin plate substrate 10 is exposed from the covering member 61, the adhesive strength between the side surface of the thin plate substrate 10 and the adhesive 110 may not be sufficient. In contrast, when the covering member 61 covers the side surface of the thin plate substrate 10 as in the strain gauge module 6, the adhesive 110 is bonded to the sixth surface 61a and the side surface of the covering member 61. Since the resins contact each other in this portion, sufficient adhesive strength can be obtained. When sufficient adhesive strength is obtained, the transferability of strain from the measurement object 120 to the film-shaped strain detection device 30 is improved, and stable strain detection is possible.

[0127] FIG. 27 is a cross-sectional view illustrating a strain gauge module according to a modified example of the sixth embodiment, and shows a cross section corresponding to FIG. 22. As shown in FIG. 27, the strain gauge module 6A is different from the strain gauge module 6 in that a connector 80 is mounted on the rewiring substrate 40. The connector 80 is electrically connected to the external connection electrodes 43a and 43b of the rewiring substrate 40 by a joining member 90 such as solder. The connector 80 is illustrated in a simplified manner, and the type and shape of the connector 80 are not important. The connector 80 has, for example, a frame-shaped resin housing in a plan view, and a plurality of external connection terminals are provided on the inner surface, outer surface, upper surface, etc. of the resin housing. By mounting the connector 80 on the rewiring substrate 40, it is possible to facilitate connection with an external circuit.

[0128] In the sixth embodiment and the modified example of the sixth embodiment, the covering member 62 may be used instead of the covering member 61. In the sixth embodiment and the modified example of the sixth embodiment, the film-shaped strain detection device 30 may have a plurality of resistors. The film-shaped strain detection device 30 may have, for example, a structure having two resistors, or a structure having four resistors as in the fifth embodiment. The rewiring substrate 40 may have a multilayer wiring structure, in which case the internal connection electrodes may be electrically connected to the external connection electrodes via the multilayer wiring structure. The metal alloy electrodes may have the bonding form shown in the third and fourth embodiments. In the first to fifth embodiments, a connector 80 may be mounted on the rewiring substrate 40.

[0129] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0130] 1,2,3,4,5,6,6A strain gauge module, 10 thin plate substrate, 10a first surface, 10b second surface, 20 adhesive, 30,30A,30B,30C film-shaped strain detection device, 31 substrate, 31a third surface, 32,32a,32b,32c,32d resistor, 33 wiring, 34a,34b,34c,34d,34e,34f,34g,34h,34i,34j,34k,34m,34n,34p terminal, 40,40A rewiring substrate, 41 substrate, 41a fourth surface, 41b fifth surface, 42a,42b,42c,42d,42e,42f internal connection electrodes, 43a,43b,43c,43d,43e,43f External connection electrode, 44, through-wiring, 45, 46, wiring, 50, 50A, metal alloy electrode, 51, meltable conductive adhesive, 52, insulating resin, 55, flat surface, 61, 62, covering member, 61a, sixth surface, 70, filler, 80, connector, 90, joining member, 110, adhesive, 120, measurement object, 120a, upper surface

Claims

1. A thin plate substrate having a first surface and a second surface opposite to the first surface, the second surface being an attachment surface to an object to be measured; a film-shaped strain detection device mounted on the first surface and including a resistor and a terminal electrically connected to the resistor on a third surface side opposite the thin plate substrate, the film-shaped strain detection device detecting a strain occurring in the measurement object; a rewiring substrate including a fourth surface facing the third surface and a fifth surface opposite to the fourth surface, the fourth surface being provided with an internal connection electrode and the fifth surface being provided with an external connection electrode; a metal alloy electrode that joins the terminal and the internal connection electrode; The surface of the metal alloy electrode on the terminal side is a flat surface, The metal alloy electrode is metal diffusion bonded to the terminal by a fusible conductive adhesive.

2. a plurality of said metal alloy electrodes; 2. The strain gauge module of claim 1, wherein a difference in height between the tallest metal alloy electrode and the shortest metal alloy electrode is 3 [mu]m or less.

3. 2. The strain gauge module according to claim 1, wherein the meltable conductive adhesive contains a metal powder, and the metal alloy electrode is metal diffusion bonded to the terminal via the metal powder.

4. 2. The strain gauge module according to claim 1, further comprising an insulating resin that covers a side surface of said metal alloy electrode, contacts said terminal, and bonds said metal alloy electrode and said terminal.

5. The strain gauge module according to claim 1 , wherein the metal alloy electrodes are non-meltable at the melting temperature of the meltable conductive adhesive.

6. The strain gauge module according to claim 1 , wherein the external connection electrodes are electrically connected to the internal connection electrodes via through-wires.

7. 5. The strain gauge module according to claim 1, further comprising a covering member that fills the area where the first surface, the third surface and the fourth surface face each other, covers the film-shaped strain detection device and the metal alloy electrode, and covers the side surface of the rewiring substrate.

8. A step of preparing a thin plate substrate having a first surface and a second surface opposite to the first surface, the second surface being used as an attachment surface to a measurement object; a step of mounting a film-shaped strain detection device, which includes a resistor and a terminal electrically connected to the resistor on a third surface side and detects strain occurring in the measurement object, on the first surface such that the third surface is on the opposite side to the thin plate substrate; a step of disposing a rewiring substrate having a fourth surface and a fifth surface opposite to the fourth surface, the fourth surface being provided with an internal connection electrode and the fifth surface being provided with an external connection electrode, such that the fourth surface faces the third surface, and bonding the terminal and the internal connection electrode via a metal alloy electrode; The joining step includes: forming the metal alloy electrode on the internal connection electrode; polishing the metal alloy electrode to form a flat surface on the side opposite the internal connection electrode; disposing a meltable conductive adhesive on the terminals; placing the rewiring substrate on the film-shaped strain detection device so that the meltable conductive adhesive contacts the flat surface; heating the fusible conductive adhesive to metal diffusion bond the metal alloy electrode to the terminal with the fusible conductive adhesive.

9. The method for producing a strain gauge module according to claim 8 , wherein in the joining step, heating is performed at a temperature at which the meltable conductive adhesive melts but the metal alloy electrodes do not melt.

Images