JP7081354B2 - Sensor holding board and sensor module - Google Patents

Description

The present invention relates to a sensor holding substrate and a sensor module, and particularly to a sensor module including a sensor having a heat generating portion or a heat sensitive portion.

As a sensor, for example, as a gas sensor for industrial applications, a highly reliable winding type gas sensor is still the mainstream. However, the wound type gas sensor has problems that it consumes a large amount of power and has low mass productivity and impact resistance. On the other hand, although MEMS type gas sensors having excellent mass productivity and impact resistance have been developed and commercialized, there is a problem in long-term stability because the volume of the gas sensitive material is small. Gas sensors using laminated ceramic technology are used in products that place importance on impact resistance and long-term stability (for example, Patent Document 1). The above-mentioned Patent Document 1 discloses a sensor for detecting NOx formed by stacking a plurality of ceramic sheets.

Japanese Unexamined Patent Publication No. 2010-286473

However, in the case of Patent Document 1, since the structure is such that a hollow portion is provided inside by sandwiching a ceramic sheet having an opening in the middle, there is a concern that the sensor becomes large and power consumption increases. There is. In order to reduce the power consumption of the sensor, it is effective to keep the heat generated by the sensor in the sensor without letting it escape to others.

An object of the present invention is to provide a sensor holding substrate and a sensor module capable of improving heat insulation.

The sensor holding substrate according to the present invention is a sensor holding substrate that holds a sensor having a heat generating portion or a heat sensitive portion, and includes a substrate main body and a plurality of electrodes having one end supported by the substrate main body, and the substrate main body. The sensor is supported at the other end of the plurality of electrodes via an insulating space between the surface and the surface.

The sensor module according to the present invention includes the sensor holding substrate and a sensor supported by the other ends of the plurality of electrodes.

According to the present invention, the heat insulating property can be improved by supporting the sensor while floating from the substrate main body and preventing the heat generated by the sensor from being directly transferred to the substrate main body.

It is a perspective view which shows the sensor module which concerns on this embodiment. 2A is a perspective view showing a sensor, FIG. 2A is a perspective view seen from the bottom surface, and FIG. 2B is a perspective view of a gas-sensitive substrate. It is a vertical end view of the sensor module which concerns on this embodiment. It is a vertical end view which shows the manufacturing method of the sensor module which concerns on this Embodiment step by step, FIG. 4A is a stage which prepared a substrate, FIG. 4D is a stage in which the sensor is fixed on the electrode, and FIG. 4E is a diagram showing a stage in which a part of the substrate body is removed by etching. It is a top view which shows the deformation example of an electrode. FIG. 6A is a vertical end view of the sensor module according to the modified example (1), FIG. 6A is a diagram showing an example using a pillar, and FIG. 6B is a diagram showing an example using a solder ball. It is a top view of the sensor module which concerns on the modification (2). FIG. 8A is a vertical cross-sectional view showing a stepwise etching process of the sensor module according to the modification (2), FIG. 8A is a diagram showing an initial stage, and FIG. 8B is a diagram showing an end stage. It is a top view which shows the sensor of the sensor module which concerns on modification (3). It is a top view which shows the sensor module which the length of the beam part which concerns on the modification (4) is different, FIG. 10A is 1.0 mm, FIG. 10B is 1.5 mm, FIG. 10C is 2.0 mm, FIG. 10D is 2.0 mm. It is a figure in the case of having a bent portion. It is a graph which shows the relationship between the length of a beam part and heat insulation.

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

(overall structure)
As shown in FIG. 1, the sensor module 10A includes a sensor holding substrate 12A and a sensor 14. The sensor holding substrate 12A has a flat plate rectangular substrate main body 16 and a first electrode 20, a second electrode 22, a third electrode 24, and a fourth electrode 26. As the substrate main body 16, a flexible printed circuit board or a Si substrate having an oxide film on the surface can be used. A plurality of pedestals 18 are formed on one surface of the substrate body 16 in the case of the present embodiment. The pedestal portion 18 is a protrusion protruding from one surface of the substrate main body 16, and two pedestal portions 18 are arranged in parallel on opposite sides of the substrate main body 16. From the viewpoint of air insulation between the sensor 14 and the sensor holding substrate 12A, the height of the pedestal portion 18 is preferably 10 μm or more.

The first electrode 20, the second electrode 22, the third electrode 24, and the fourth electrode 26 are fixed to the pedestal portion 18 one by one. In the present specification, the first electrode 20, the second electrode 22, the third electrode 24, and the fourth electrode 26 are collectively referred to as electrodes unless otherwise distinguished. The electrodes are made of a conductive material such as copper or gold. The electrode has a pad portion 21 fixed to the pedestal portion 18 and a beam portion 23 integrally formed with the pad portion 21 and protruding toward the center of the substrate main body 16. The pad portion 21 preferably has a large surface area because it is electrically connected to an external wiring (not shown). In the case of this figure, the pad portion 21 has a square shape. The beam portion 23 has a vertically long rectangular shape whose width direction length is shorter than the length of one side of the pad portion 21 in order to suppress heat conduction from the sensor 14 to the substrate main body 16, and the base end is the center of one side of the pad portion 21. It is connected to the. The beam portion 23 has, for example, a length in the width direction of 500 to 1000 μm and a thickness of 0.2 to 1.0 μm.

The sensor 14 is a gas sensor having a flat plate rectangular shape and having a heat generating portion (not shown in this figure). The sensor 14 is arranged in the center of the substrate main body 16. The sensor 14 is held by the first electrode 20, the second electrode 22, the third electrode 24, and the fourth electrode 26 without contacting the substrate main body 16.

As shown in FIG. 2A, the sensor 14 has a gas-sensitive substrate 32 and a heating substrate 34 provided so as to be superimposed on the gas-sensitive substrate 32. The heating substrate 34 has a total of four first mounting pads 30, a second mounting pad 31, a third mounting pad 33, and a fourth mounting pad 35 provided in the vicinity of the four corners of the surface. The gas-sensitive substrate 32 is a ceramic substrate containing SnO ₂ (tin oxide), ZnO (zinc oxide), and Fe ₂ O ₃ (ferrous trioxide) as gas-sensitive materials.

The heat generating portion 36 is provided on the surface of the heating substrate 34. The heat generating portion 36 is a metal film formed of a heating element material such as gold or platinum. The heating substrate 34 is a ceramic substrate. The heat generating portion 36 is formed by meandering the surface of the heating substrate 34 in a zigzag manner so as to heat the entire gas-sensitive substrate 32. One end of the heat generating portion 36 is integrally formed with the first mounting pad 30, and the other end is integrally formed with the second mounting pad 31.

As shown in FIG. 2B, the gas sensitive substrate 32 has a first electrode pad 37, a second electrode pad 39, and a first comb-shaped electrode 41 and a second comb-shaped electrode 43. The first electrode pad 37 is integrally formed with the first comb-shaped electrode 41, and the second electrode pad 39 is integrally formed with the second comb-shaped electrode 43. The third mounting pad 33 is connected to the first electrode pad 37 through a through hole (not shown). Similarly, the fourth mounting pad 35 is connected to the second electrode pad 39 through a through hole (not shown).

The sensor 14 can be formed by a laminated ceramic technique. The size of the sensor 14 is not particularly limited, but is, for example, one side length of 0.2 to 1.0 mm and a thickness of 0.02 to 0.1 mm. The sensor 14 is mounted on the sensor holding substrate 12A with the heating substrate 34 on the lower side and the gas sensing substrate 32 on the upper side.

As shown in FIG. 3, the sensor 14 is supported by the tip of the beam portion 23 on both side portions. The beam portion 23 is a free end whose base end is supported by the substrate main body 16 via the pad portion 21 and the pedestal portion 18 and whose tip is not supported by the substrate main body 16, and has a so-called cantilever structure.

The first mounting pad 30 and the second mounting pad 31 of the sensor 14 and the tip of the beam portion 23 are joined to each other via the joining portion 28. Although not shown in this figure, the third mounting pad 33 and the fourth mounting pad 35 of the sensor 14 are similarly joined to the tip of another beam portion 23 via the joining portion 28. For the joint portion 28, for example, solder can be used. Further, the joint portion 28 contains any one of AuSn, AuAl and AuAg. By using the eutectic material for the joint portion 28, the sensor module 10A can be used stably even under conditions of use at a higher temperature.

The sensor 14 arranged above the surface of the substrate body 16 is supported by the beam portion 23 in a state where the heat insulating space 19 is formed between the bottom surface 15 and one surface of the substrate body 16. As described above, the sensor 14 is supported in a floating state with respect to the substrate main body 16. In the case of this figure, the first mounting pad 30 is the third electrode 24, the second mounting pad 31 is the second electrode 22, the third mounting pad 33 is the fourth electrode 26, and the fourth mounting pad 35 is the first electrode 20. Each is joined. A heating voltage is applied between the second electrode 22 and the third electrode 24. A detection voltage is applied between the first electrode 20 and the fourth electrode 26.

The manufacturing method of the sensor module 10A will be described with reference to FIG. First, a copper polyimide substrate in which a copper film 40 is laminated on a substrate on which a conductive film is laminated, for example, a substrate main body 16 made of polyimide is prepared (FIG. 4A). As the copper polyimide substrate, a general-purpose substrate used in a flexible printed circuit can be used, so that the cost can be reduced.

Next, the photoresist 42 is selectively formed on the copper film (FIG. 4B). After that, the copper film 40 in the portion where the photoresist 42 is not formed is removed by etching (FIG. 4C). Then, the photoresist 42 is removed using an organic solvent such as acetone. At this stage, the pad portion 21 and the beam portion 23 are formed on the substrate main body 16.

Subsequently, the sensor 14 is joined onto the beam portion 23 via the joint portion 28 (FIG. 4D). When mounting the sensor 14 on the board body 16, a mounting machine for arranging electronic components on the printed circuit board can be used. Finally, when the surface of the substrate body 16 including the area directly under the sensor 14 is etched, the portion other than the pad portion is isotropically etched to form the pedestal portion 18 (FIG. 4E). As described above, the beam portion 23 of the cantilever structure is formed, and the sensor module 10A having the sensor 14 supported by the beam portion 23 can be formed.

(Action and effect)
At the time of gas detection, the sensor module 10A heats the heat generating portion 36 by applying a voltage from the second electrode 22 and the third electrode 24 through the second mounting pad 31 and the first mounting pad 30. As a result, the gas sensitive substrate 32 is heated to a temperature suitable for detecting the gas to be detected. When the sensor module 10A is exposed to a gas containing a gas to be detected in this state and the gas-sensitive substrate 32 is exposed to the gas, the electric resistance value of the gas-sensitive substrate 32 fluctuates. An output signal based on the electric resistance value of the gas-sensitive substrate 32 is output from the fourth electrode 26 and the first electrode 20 through the third mounting pad 33 and the fourth mounting pad 35.

Since the sensor 14 can be formed by the laminated ceramic technology, it can be miniaturized. As the sensor 14 is made smaller, the heat generating portion 36 can also be made smaller, so that the sensor module 10A can reduce the power consumption. Further, since the laminated ceramic technique is a technique widely used in various electronic components, the sensor 14 can improve mass productivity and yield while ensuring reliability.

Since the sensor 14 is supported in a floating state from the substrate main body 16, it is possible to prevent the heat generated by the heated heat generating portion 36 from being directly transferred to the substrate main body 16 and improve the heat insulating property. In this way, the sensor module 10A can further reduce the power consumption by improving the heat insulating property of the sensor 14.

Since the beam portion 23 supporting the sensor 14 is formed so that the length in the width direction is shorter than the length of one side of the pad portion 21, the heat generated by the heated heat generating portion 36 is suppressed from escaping to the substrate main body 16. do. In this way, the sensor module 10A can further improve the heat insulating property of the sensor 14. Since the beam portion 23 has a larger cross-sectional area than the bonding wire used in the conventional gas sensor, the sensor module 10A has excellent mechanical strength and high impact resistance.

(Modification example)
The present invention is not limited to the above embodiment, and can be appropriately modified within the scope of the gist of the present invention.

For example, as shown in FIG. 5, the electrode 44 may have a pad portion 21 and a beam portion 46 having a tapered shape toward the tip end from the base end connected to the pad portion 21. In the case of this figure, the beam portion 46 is integrally formed with the first beam portion 48, the second beam portion 50, and the third beam portion 52 from the base end. The second beam portion 50 is formed to have a shorter length in the width direction than the first beam portion 48. The third beam portion 52 is formed to have a shorter length in the width direction than the second beam portion 50. A joining pad 54 is provided at the tip of the third beam portion 52. The joining pad 54 preferably has the same size as the first mounting pad 30, the second mounting pad 31, the third mounting pad 33, and the fourth mounting pad 35 provided on the sensor 14. From the viewpoint of efficiently heating the heat generating portion 36, the material of the beam portion 46 is preferably a conductive material having a smaller electric resistance per unit length than the heat generating portion 36. On the other hand, if the cross-sectional area of the beam portion 46, that is, the length or thickness in the width direction is increased, the heat generated by the heated heat generating portion 36 tends to escape to the substrate main body 16. As in this modification, the tapered shape of the beam portion 46 prevents the beam portion 46 from generating heat in the vicinity of the pad portion 21, and the heat generated by the heated heat generating portion 36 is transmitted through the beam portion 46 to the substrate. It is possible to further suppress the escape to the main body 16.

In the case of the above embodiment, the case where the sensor 14 is supported by the beam portion 23 of the cantilever structure in a floating state from the substrate main body 16 has been described, but the present invention is not limited to this. For example, as shown in FIG. 6A, the sensor module 10B has a columnar portion 62 connected to the pad portion 21 and extending in the direction perpendicular to the surface of the substrate main body 16. The sensor 14 is joined via a joint portion (not shown) at the tip of the columnar portion 62. The columnar portion is formed of a conductive material similar to that of the electrode 21, and the height thereof is preferably 200 to 1000 μm. In the case of this modification, the opening of the hole formed in the substrate body 56 can be made smaller than that of the sensor 14.

Further, as shown in FIG. 6B, the sensor module 10C has a solder ball 64 connected to the pad portion 21. The sensor 14 is joined at the upper end of the solder ball 64. The height of the solder balls after joining is preferably 100 to 500 μm. Since the sensor modules 10B and 10C can support the sensor 14 in a floating state from the substrate main body 56, the same effect as that of the first embodiment can be obtained.

In the above embodiment, a method of manufacturing the sensor module 10A by joining one sensor 14 to one substrate main body has been described, but the present invention is not limited to this. A plurality of electrode groups consisting of a set of four are formed on a board body having a larger area in which a plurality of sensor modules 10A can be manufactured, sensors 14 are joined to each set, and a pedestal portion 18 is formed at an appropriate position on the board body. After that, the sensor module 10A is cut out at a position corresponding to one set. By manufacturing in this way, a plurality of sensor modules 10A can be manufactured at one time.

In the case of the above embodiment, the case where the sensor 14 is supported by four electrodes (beam portions) has been described, but the present invention is not limited to this, and two or three electrodes (two or three electrodes) according to the configuration of the sensor 14 ( It may be supported by a beam portion).

In the above embodiment, the case where the sensor 14 is a gas sensor has been described, but for example, the sensor 14 can be applied to a flow sensor, a temperature sensor, and a bolometer. Further, the sensor 14 can be applied to an infrared sensor or the like as an example having a heat sensitive portion. Since the sensor module has high heat insulating properties, the detection sensitivity of the sensor 14 having the heat sensitive portion can be improved.

With reference to FIG. 7, a structure capable of optimizing the manufacturing process will be described. The width direction length D1 of the sensor 14 of the sensor module 10D shown in this figure is 1 to 3 times the width direction length D2 of the beam portion 23. As shown in FIG. 8A, when the surface of the substrate body 16 is isotropically etched, the length D1 is longer than the length D2, so that the beam portion 23 separates from the substrate body 16 before the sensor 14. Further isotropic etching causes the sensor 14 to move away from the substrate body 16 as shown in FIG. 8B. Therefore, when the width direction length D1 of the sensor 14 is closer to the width direction length D2 of the beam portion 23, the total etching time can be shortened. The width direction length of the sensor 14 means the length between the opposite long sides when the sensor 14 is rectangular, and the length between the opposite sides when the sensor 14 is square. In the case of this modification, the length D1 is preferably 1 to 3 times, more preferably 1 to 2 times, the length D2 in order to optimize the manufacturing process. Most preferably, the length D1 is equal to the length D2.

As shown in FIG. 9, the sensor 70 may have a shape in which a plurality of openings 72 are arranged in a grid pattern. The opening 72 is an opening that penetrates the sensor 14 in the thickness direction. In the case of this figure, the opening 72 is a quadrangle in a plan view, but the present invention is not limited to this, and may be, for example, a triangle or a hexagon. In the case of this figure, the distance between the openings 72 and the distance between the outer edge of the sensor 70 and the opening 72 is the width length D1. By limiting the width and length D1 to the above range, the same effect as that of the sensor module 10D shown in FIG. 7 can be obtained.

When the sensor has a heat generating portion, the heat generated in the heat generating portion escapes from the pad portion to the substrate body through the beam portion. Similarly, when the sensor has a heat-sensitive portion, the heat generated by the amount of heat given to the sensor from the outside escapes from the pad portion to the substrate main body through the beam portion. In either case, heat escapes from the sensor to the substrate body through the beam portion and the pad portion, which causes an increase in power consumption and a decrease in detection sensitivity. In order to reduce the heat escaping from the pad portion to the substrate body through the beam portion, it is effective to increase the length of the beam portion.

By providing the bent portion of the beam portion, the length of the beam portion can be made longer than the linear distance from the pad portion to the sensor. The bent portion is preferably located on the same plane as the pad portion. The coplanar is not limited to the completely coplanar, but includes a plane slightly deviated from the completely coplanar in the thickness direction. The sensor module can realize heat insulation and miniaturization by providing a bent portion in the beam portion. Further, by providing the bent portion in the beam portion, it is possible to reduce the stress generated between the sensor and the joint portion when the beam portion is thermally expanded as compared with the beam portion having the same length and no bent portion. ..

Using the sensor module model shown in FIG. 10, the relationship between the length of the beam portion from the pad portion to the sensor and the heat insulating property was investigated by simulation. The material of the sensor was Al ₂ O ₃ , the environment was set to natural convection, and the temperature of the pad part was calculated when the temperature of the sensor was 400 ° C. The sensor module 10E of FIG. 10A has a beam portion 74 having a length of 1.0 mm, the sensor module 10F of FIG. 10B has a beam portion 76 length of 1.5 mm, and the sensor module 10G of FIG. 10C has a beam portion 78 length. The sensor module 10H of 2.0 mm and FIG. 10D is an example in which the length of the beam portion 80 is 2.0 mm and the beam portion 80 has two bent portions 82. The result is shown in FIG. In FIG. 11, the horizontal axis is the length of the beam portion (mm), the vertical axis on the left side is the temperature (° C.) of the pad portion, the vertical axis on the left side is the power consumption ratio to the power consumption of the beam portion length of 1 mm, and the plot of ○ is. The temperature of the pad and the plot of x indicate the power consumption. From this figure, it was found that the shorter the length of the beam portion, the higher the temperature and power consumption ratio of the pad portion, and the lower the heat insulating property. Further, when the length of the beam portion is about 2 mm, the effect of reducing the temperature of the pad portion and the effect of reducing the power consumption are saturated, and even if the beam portion has a bent portion, the temperature of the pad portion does not change much. From this, the sensor module can realize heat insulation and miniaturization by forming a bent portion in the beam portion and making the length longer than that of the linear beam portion.

10A, 10B, 10C Sensor module 12A Sensor holding board 14 Sensor 15 Bottom surface 16 Board body 18 Pedestal 19 Insulated space 20, 22, 24, 26 1st to 4th electrodes (electrodes)
21 Pad part 23 Beam part 28 Joint part

Claims (7)

A sensor holding substrate that holds a sensor having a heat generating portion or a heat sensitive portion.
With the board body
The substrate body is provided with a plurality of electrodes supported at one end, and the substrate body is provided with a plurality of electrodes.
The sensor is supported at the other ends of the plurality of electrodes via a heat insulating space between the substrate and the surface of the main body.
The electrode has a pad portion supported by a pedestal portion protruding from the surface of the substrate main body, and a beam portion integrally formed with the pad portion and protruding into the heat insulating space.
The beam portion has a tapered shape from one end to the other end.
Sensor holding board. The sensor holding substrate according to claim 1 , wherein the beam portion has at least one bent portion. A sensor holding substrate that holds a sensor having a heat generating portion or a heat sensitive portion.
With the board body
With a plurality of electrodes supported at one end by the substrate body
Equipped with
The sensor is supported at the other ends of the plurality of electrodes via a heat insulating space between the substrate and the surface of the main body.
The electrode has a pad portion supported by a pedestal portion protruding from the surface of the substrate main body, and a beam portion integrally formed with the pad portion and protruding into the heat insulating space.
A joint portion arranged between the beam portion and the sensor portion is provided at the tip of the beam portion, and the joint portion includes any of AuSn, AuAl, and AuAg.
Sensor holding board. The sensor holding substrate according to claim 3, wherein the beam portion has at least one bent portion. A sensor module including a sensor holding substrate and a sensor having a heat generating portion or a heat sensitive portion held by the sensor holding substrate .
The sensor holding substrate includes a substrate main body and a plurality of electrodes supported at one end by the substrate main body, and the sensor is provided at the other end of the plurality of electrodes via a heat insulating space between the substrate main body and the surface of the substrate main body. Support,
The widthwise length of the sensor is 1 to 3 times the widthwise length of the electrode.
Sensor module. The sensor module according to claim 5, wherein the electrode has a columnar portion extending in a direction perpendicular to the surface of the substrate main body. The sensor module according to claim 5, wherein the sensor holding substrate supports the sensor by joining the sensor holding substrate at the other end of the electrode with a solder ball.

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