JPH10253476A - Capacitance type pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor that, although of a simple structure, has a dielectric strength capable of withstanding high voltages of lighting surges, etc., and does not leak a gas to be measured to the outside even at a high temperature. SOLUTION: A bottom case 10A, in which an insulating part 50 made of a resin and a heat resistant part 40 made of a metal are integrated together, is provided, a pressure inlet 15 is bored in the heat resistant part 40 of the bottom case 10A, a groove 18 provided in the heat resistant part 40 is covered with a base 4 made of ceramics, and a pressure inlet passage is formed. A pressure sensor chip 2 and an IC chip 3 are mounted on top of the base 4. Therefore the part with which a gas to be measured makes contact is made from metal or ceramics and does not leak the gas to be measured to the outside even at high temperatures. The insulating part 50 made of resin and the base 4 made of ceramics electrically isolate circuit parts including the pressure sensor chip 2 and the IC chip 3 from high voltages applied to the case 10A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type pressure sensor for detecting a displacement of a diaphragm receiving a measured pressure as a change in capacitance.

[0002]

2. Description of the Related Art Conventionally, a capacitance type pressure sensor has been generally used in the field of pressure measurement. The capacitance-type pressure sensor includes a diaphragm that is displaced by a measurement pressure, an electrode for detecting the displacement of the diaphragm as a change in capacitance, and a change in the capacitance of the electrode that is detected by a predetermined electric signal. And a pressure conversion unit configured to convert the measured pressure into an electric signal. Such a capacitance type pressure sensor cannot perform accurate measurement when affected by stray capacitance or an external electric field. For example, if there is a stray capacitance near the pressure converter, the electric field due to the stray capacitance fluctuates the amount of charge stored in the electrodes of the pressure converter, so that the capacitance corresponding to the pressure received by the diaphragm can be accurately detected. And pressure cannot be accurately measured. For this reason, as shown in FIG. 23 of JP-A-7-286925, the entire pressure sensor is covered with a shield plate, or as shown in FIGS. It is covered with a shield plate, which prevents stray capacitance and external electric field from affecting the electrodes, and enables accurate pressure measurement.

Here, if the case that covers the pressure conversion portion of the pressure sensor is made of metal, the case itself will have a shielding effect, and will be affected by stray capacitance and an external electric field without providing a separate shield plate. And accurate pressure measurement can be performed. Moreover, the metal case is resistant to heat, and if a metal case is employed, even if the internal pressure conversion unit is destroyed by heat such as fire, external leakage of the gas to be measured can be prevented. . For example, when a pressure sensor is provided for gas pressure measurement of a gas meter, if a metal pressure sensor case is adopted, even if a fire occurs, gas leakage can be prevented, and gas explosion and gas poisoning can be prevented. And other secondary disasters can be prevented.

[0004]

In such a pressure sensor having a metal case, since the case itself has no electrical insulation, when an instantaneous high voltage is applied to the case, an internal pressure conversion unit is formed. Has a problem that it cannot be mounted in a place where high voltage may be applied. For this reason, a pressure sensor with a metal case must be sufficiently insulated against high voltage when it is used as a gas meter component that is attached to metal piping where instantaneous high voltage such as lightning surge may be applied. It is necessary to take measures. On the other hand, in a pressure sensor having a case made of a synthetic resin, a sufficient withstand voltage is secured by the case itself, so that the pressure sensor can be installed in a place where high voltage may be applied. However, there is a problem that the heat resistance as described above cannot be sufficiently secured. If the structure of the pressure sensor is complicated in order to improve both the withstand voltage and the heat resistance, there is a problem that the number of assembly steps in a factory increases and the productivity of the pressure sensor is hindered.

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitance type pressure sensor which has a withstand voltage capable of withstanding a high voltage such as a lightning surge, and which does not leak a gas to be measured even at a high temperature, while having a simple structure. To provide.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a peripheral portion of a diaphragm made of one of a semiconductor and a metal is sandwiched from both sides in a state where a gap is formed so that the central portion can be displaced. A pair of insulators are provided, and one of the pair of insulators is formed with a measurement pressure introduction hole for introducing a measurement pressure, and the other of the pair of insulators has a reference pressure introduction hole for introducing a reference pressure. A hole is formed, and an electrode is formed on at least one of the pair of insulators on a surface facing the diaphragm, and the displacement of the diaphragm due to the measurement pressure is changed by the diaphragm and the electrode. A pressure sensor chip for detecting from a change in capacitance between the pressure sensor chip and a pressure introducing hole for accommodating the pressure sensor chip and for introducing the measurement pressure therein is provided. And a signal processing circuit that converts the capacitance of the pressure sensor chip into a predetermined electric signal, wherein the case includes a resin insulating portion and a metal. The bottom case has a bottom case integrated with a heat-resistant portion made of, the pressure-introducing hole is provided in the heat-resistant portion of the bottom case, the pressure sensor chip,
Along with being disposed at a position off the pressure introduction hole, and fixed to the bottom case via a ceramic heat-resistant substrate, between the heat-resistant portion of the bottom case and the heat-resistant substrate, from the pressure introduction hole. A pressure introduction path extending to the pressure sensor chip is formed.

In the present invention, a pressure introducing hole is provided in the heat-resistant portion of the bottom case, and the gas to be measured is introduced from the pressure introducing hole. Then, the gas to be measured introduced from the pressure introduction hole reaches the pressure sensor chip through a pressure introduction path formed between the heat-resistant portion of the bottom case and the heat-resistant substrate. Here, the portion to be contacted by the gas to be measured is formed of either metal or ceramic, and the insulator of the pressure sensor chip can be made of ceramic, glass having heat resistance, or the like. All parts have sufficient heat resistance. This allows
Even with a simple structure, the gas to be measured does not leak outside even at high temperatures. In addition, the resin insulating portion of the bottom case and the heat-resistant substrate made of ceramic have excellent withstand voltage and protect the pressure sensor chip and the signal processing circuit from the high voltage applied to the case, so that they can withstand high voltage such as lightning surge. Dielectric strength is ensured.

In the above, it is preferable that the material of the insulating portion of the bottom case is a thermoplastic resin, particularly a crystalline polymer. By doing so, the bottom case in which the insulating part and the heat resistant part are integrated can be easily formed by insert molding in which the metal part serving as the heat resistant part is put in a mold in advance and the productivity of the pressure sensor is increased. Will be improved. Moreover, the insulating part made of thermoplastic resin is
Even when expanded at high temperatures, it becomes soft and easily fluidized by heat, and does not generate a force to separate them from the heat-resistant part or heat-resistant substrate of the bottom case. The measurement gas does not leak outside. The pressure sensor chip is disposed between a pair of conductive shield surfaces disposed in parallel with the electrodes, and one of the pair of conductive shield surfaces is formed on a surface of the heat-resistant substrate. It is preferable that the metal plate is a metal film, and the other is a metal plate supported by a column standing on the substrate. In this way, a shield that covers the pressure sensor chip is formed. With this shield, the pressure sensor chip is not affected by stray capacitance or an external electric field, and accurate pressure measurement can be performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show a capacitance-type pressure sensor 1 according to an embodiment of the present invention. The pressure sensor 1 measures the pressure of a gas supplied from a fuel gas company, and is used as a part of a gas meter that measures the usage of the gas. The pressure sensor 1 includes a pressure sensor chip 2 for detecting gas pressure, an IC chip 3 as a signal processing circuit for electrically processing a pressure signal obtained by the pressure sensor chip 2, And a case 10 for accommodating the pressure sensor chip 2 and the IC chip 3. Among these, the pressure sensor chip 2 and the IC chip 3 are mounted side by side on a substrate 4 which is a heat-resistant substrate made of ceramic having electrical insulation. The case 10 includes a bottom case 10A to which the substrate 4 is fixed. A substantially box-shaped upper case (not shown) that covers the upper surface in the figure can be attached to the bottom case 10A as necessary.

The bottom case 10A has a joint portion 12 protruding near the center of a lower surface 11 in the figure. The joint section 12 is for connecting to a pipe or the like through which a gas to be measured flows. Both ends in the longitudinal direction of the bottom case 10A serve as attachment portions 13 for attachment to a gas meter or the like. The mounting portion 13 is provided with a bolt insertion hole 14 through which a bolt is inserted. Joint of bottom case 10A
At the center of 12, a pressure introduction hole 15 for introducing gas pressure into the pressure sensor 1 is provided. On the upper surface 16 of the bottom case 10A in the figure, two types of rising portions 17A and 17B are provided so as to surround the periphery of the substrate 4. Here, the pressure sensor chip 2 is a bottom case 10A
Are arranged at positions offset from the center in the peripheral direction.
A groove 18 is provided on the bottom surface of the bottom case 10A surrounded by the rising portions 17A and 17B. This groove 18 is
It extends from 15 to just below the pressure sensor chip 2 and is covered by a substrate 4 arranged above in the figure. The groove 18 serves as a pressure introduction path extending from the pressure introduction hole 15 to the pressure sensor chip 2.

The substrate 4 is provided with a communication hole 19 provided at a position directly below the pressure sensor chip 2. The substrate 4 is joined to the bottom case 10A so as to withstand the pressure of the gas introduced into the groove 18. In addition, the substrate 4 is provided with a plurality of external connection terminals 20, as shown in FIGS. These external connection terminals 20 are provided for transmitting and receiving signals to and from the outside of the pressure sensor 1 and for receiving a power supply voltage. These external connection terminals
Of the 20 terminals, the terminal 20A closest to the pressure sensor chip 2 is:
It is a ground terminal. A metal shield plate 21 covering the pressure sensor chip 2 is attached to the terminal 20A so as to be parallel to the substrate 4. Here, the external connection terminal 20A is a column supporting the metal shield plate 21.

The surface 4A of the substrate 4 on the pressure sensor chip 2 side is
It has a two-layer structure. The pattern wiring 22 is provided on the surface 4A of the pressure sensor chip 2 by thick film printing. The electrical wiring between the pressure sensor chip 2, the IC chip 3, and the external connection terminal 20 is mainly formed by the pattern wiring 22. As shown in FIG. 6, the pattern wiring 22 is an insulating film provided so as to cover the surface 4A of the substrate 4.
Formed on 22A. A shield layer 23 formed by thick film printing is formed below the insulating film 22A in the drawing. The shield layer 23 is disposed at a position corresponding to the pressure sensor chip 2 as shown in FIGS. 3 and 5, and is formed so as to cover the pressure sensor chip 2. The shield layer 23 and the shield plate 21 are electrically connected to each other, and the pressure sensor chip 2 is disposed between the shield layer 23 and the shield plate 21. Shielded.

As shown in FIG. 6, a pressure sensor chip 2 has a planar insulator 3 having electrodes (not shown) formed on both front and back sides of a diaphragm 31 having a central portion recessed on both sides.
2, 33 are integrated. The surface of the pressure sensor chip 2 on the insulator 33 side is adhered to the substrate 4 with an adhesive 34. The electrodes of the insulators 32 and 33 are made parallel to the substrate 4 so that the shield layer 23 and the shield
21 is also parallel. The diaphragm 31 is formed from a semiconductor (silicon single crystal). The periphery of the diaphragm 31 is sandwiched between insulators 32 and 33 from both sides. At this time, a void is provided between the central portion of the diaphragm 31 and the insulators 32 and 33 due to the recess, so that the diaphragm 31 can be displaced vertically in the drawing. Each of the insulators 32 and 33 is formed of heat-resistant glass. Here, as the heat-resistant glass forming the insulators 32 and 33 and the ceramic forming the substrate 4, those having similar thermal expansion coefficients to each other are employed. Thereby, the force due to thermal expansion acting between the pressure sensor chip 2 and the substrate 4 at a high temperature is reduced. Each of the insulators 32 and 33 has a diaphragm 31
The above-mentioned electrode is formed on the surface facing the substrate. These electrodes are electrically connected to the pattern wiring 22 of the substrate 4 by bonding wires 35.

Of the insulators 32 and 33, the insulator 33 at the bottom of the figure
A measurement pressure introduction hole 36 for introducing a measurement pressure is formed in the insulator 32, and a reference pressure introduction hole 37 for introducing a reference pressure is formed in the upper insulator 32 in the figure. Here, the adhesive 34 for bonding the pressure sensor chip 2 to the substrate 4 allows the space between the substrate 4 and the insulator 32 to be connected to the communication hole 19 of the substrate 4 and the measurement pressure introduction hole of the insulator 32 even at a high temperature. It is completely sealed over the entire circumference of 36. As a result, the measurement pressure introduced from the pressure introduction hole 15 is reliably transmitted to the diaphragm 31, and the displacement caused by the measurement pressure changes the capacitance between the diaphragm 31 and the electrodes of the insulators 32 and 33, and the measurement pressure is changed. Can be accurately detected.

As shown in FIGS. 7 to 9, the bottom case 10A is formed by integrating a heat-resistant portion 40 made of aluminum die-casting and an insulating portion 50 made of synthetic resin. Heat resistant part 40
Is formed by rounding the corners of an elongated strip extending to both ends in the longitudinal direction of the pressure sensor 1. Heat resistant part 40
Is a thick portion 41 whose thickness is the thickest. The thick portion 41 has a flat surface 42 exposed on the surface 16 side of the bottom case 10A. The shape of the exposed flat surface 42 is an oval shape. The substrate 4 is bonded to the flat surface 42 and the above-described groove 18 is formed. Heat resistant part
In the thick portion 41 of 40, the joint portion 12 and the pressure introducing hole 15 described above are formed on the surface 11 side of the bottom case 10A. Here, when the substrate 4 is bonded to the bottom case 10A, the groove is formed.
Due to 18, a pressure introducing passage extending from the pressure introducing hole 15 to the pressure sensor chip 2 is formed between the heat resistant portion 40 and the substrate 4 (see FIG. 1). Both end portions of the heat-resistant portion 40 have the second largest thickness after the thick portion 41, and both the front surface and the back surface are exposed from the insulating portion 50. ing. The part between the center part and both ends of the heat-resistant part 40 is the thinnest part
43.

The insulating portion 50 extends over substantially the entire bottom case 10A, covers the entire side surface of the heat-resistant portion 40 extending in the longitudinal direction, and has a heat-resistant portion 40 on the side opposite to the surface 11 of the bottom case 10A. Cover the surface of the thin portion 43. On the surface of the insulating portion 50, the above-described two types of rising portions 17A and 17B are integrally formed. Here, the bottom case 10A is configured such that after a metal component to be the heat-resistant part 40 is put in a mold in advance, the heat-resistant part 40 and the insulating part 50 are formed by insert molding in which the crystalline polymer filled in the mold is filled. It is integrally molded. At this time, on the side surface of the heat resistant portion 40, a protruding piece 44 protruding toward the insulating portion 50 and a concave portion 45 concaved inward are provided. The protruding pieces 44 and the concave portions 45 increase the adhesive strength of the resin forming the insulating portion 50 to the heat-resistant portion 40, and the heat-resistant portion 40 and the insulating portion 50 are firmly integrated.

According to the above-described embodiment, the following effects can be obtained. That is, the pressure introducing hole 15 is provided in the heat-resistant portion 40 made of aluminum die-casting of the bottom case 10A, and the pressure from the pressure introducing hole 15 to the pressure sensor chip 2 is provided between the heat-resistant portion 40 made of aluminum die-casting and the ceramic substrate 4. Providing an introduction path, and an insulator for the pressure sensor
Since 32 and 33 are made of heat-resistant glass, and the diaphragm 31 is made of semiconductor (single-crystal silicon), sufficient heat resistance is ensured in all parts of the pressure sensor 1 where gas contacts. Although having a simple structure, it is possible to prevent the gas from leaking to the outside even at a high temperature.

Further, the insulating portion 50 of the bottom case 10A is formed of a synthetic resin having excellent withstand voltage, and the pressure sensor chip 2 is mounted on a ceramic substrate 4 having excellent withstand voltage.
And an IC chip 3, and a conductive die-cast bottom case is formed by the insulating portion 50 and the substrate 4.
From 10A, pressure sensor chip 2 and IC chip 3
Is electrically isolated, the circuit portion including the pressure sensor chip 2 and the IC chip 3 is protected from high voltage applied to the case 10, and withstands high voltage such as lightning surge. High dielectric strength can be ensured.

Further, the insulators 32 and 33 and the substrate 4 are formed of materials having similar thermal expansion coefficients to each other, and a force due to thermal expansion is applied between the pressure sensor chip 2 and the substrate 4 at a high temperature. Since it does not act, the pressure sensor chip 2 does not come off the substrate 4 due to the heat, and from this point, it is possible to prevent the gas from leaking to the outside at high temperatures.

Since a crystalline polymer is used as the material of the insulating portion 50 of the bottom case 10A, the insulating portion 50 and the heat-resistant portion 40 of the bottom case 10A are formed by insert molding.
Can be easily integrally formed, the productivity of the pressure sensor 1 can be improved, and when heat is applied to the insulating portion 50, the insulating portion
50 is softened and fluidized, so that even when expanded at high temperatures, it does not generate a force to separate them from the heat-resistant portion 40 of the bottom case 10A or the substrate 4, and the airtightness of the pressure sensor 1 at high temperatures. This also prevents gas leakage to the outside at high temperatures.

Further, since the pressure sensor chip 2 is arranged between the shield layer 23 and the shield plate 21 arranged in parallel with its electrodes, the pressure sensor chip 2 is not affected by stray capacitance or an external electric field, so that the pressure sensor chip 2 can be accurately measured. Pressure measurement can be performed.

On the side surface of the heat-resistant portion 40, a protruding piece 44 protruding toward the insulating portion 50 and a concave portion 45 depressed inward are provided.
The protruding pieces 44 and the concave portions 45 increase the adhesive strength of the resin forming the insulating portion 50 to the heat-resistant portion 40, so that the heat-resistant portion 40 and the insulating portion 50, which are made of different materials, are firmly integrated, and are robust. A simple bottom case 10A can be obtained.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes may be made without departing from the scope of the present invention. It is possible. For example, the heat-resistant portion is not limited to the one made of aluminum die-cast, and may be made of another metal. Here, in forming the heat-resistant portion, not only a casting method using a mold, but also other methods such as press forming and mechanical cutting may be used.

Further, as the ceramic heat-resistant substrate,
The signal processing circuit is not limited to a size that can be mounted with both the pressure sensor chip and the signal processing circuit, but can be mounted with only the pressure sensor chip. May be attached. Furthermore, as the bottom case, by insert molding,
The invention is not limited to the one in which the heat-resistant metal part and the insulating part made of resin are integrally formed, but may be one in which the heat-resistant part and the insulating part are bonded with an adhesive.

The diaphragm of the pressure sensor chip is not limited to the one made of a semiconductor, but may be a metal one. Furthermore, as an insulator for the pressure sensor chip,
The material is not limited to the one made of heat-resistant glass, but may be made of another glass or ceramic. Further, the pressure sensor chip is not limited to one in which electrodes are provided on both insulators sandwiching the diaphragm, and may be one in which electrodes are provided only in one of a pair of insulators sandwiching the diaphragm. Further, the attachment of the pressure sensor chip to the substrate 4 is not limited to the bonding using an adhesive, but may be a mechanical connection using a screw or the like. The present invention is not limited to a pressure sensor used as a part of a gas meter, but can be applied to a pressure sensor used for other purposes.

[0026]

As described above, according to the present invention, it is possible to ensure a dielectric strength withstanding a high voltage such as a lightning surge while having a simple structure, and to prevent the gas to be measured from leaking outside even at a high temperature. Can be

[Brief description of the drawings]

FIG. 1 is a sectional view showing a pressure sensor according to an embodiment of the present invention.

FIG. 2 is a different sectional view showing the pressure sensor of the embodiment.

FIG. 3 is a plan view showing a heat-resistant substrate of the pressure sensor of the embodiment.

FIG. 4 is a side view showing a heat-resistant substrate of the pressure sensor of the embodiment.

FIG. 5 is a bottom view showing a heat-resistant substrate of the pressure sensor of the embodiment.

FIG. 6 is an enlarged sectional view showing the pressure sensor chip of the embodiment.

FIG. 7 is a plan view showing a main part of the case of the embodiment.

FIG. 8 is a sectional view taken along line VIII-VIII in FIG. 7;

9 is a sectional view taken along line IX-IX in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Pressure sensor 2 Pressure sensor chip 3 IC chip which constitutes a signal processing circuit 4 Substrate as heat-resistant substrate 10 Case 10A Bottom case 15 Pressure introduction hole 18 Groove forming pressure introduction passage 20A External connection terminal which becomes support 21 Conductivity Shield plate as metal plate forming shield surface 23 Shield layer as metal film forming conductive shield surface 31 Diaphragm 32, 33 Insulator 36 Measurement pressure introduction hole 37 Reference pressure introduction hole 40 Heat resistant part 50 Insulation part

Claims (6)

[Claims] 1. A pair of insulators which sandwich a peripheral edge portion of a diaphragm from both sides in a state where a gap is formed so that a central portion of a diaphragm made of one of a semiconductor and a metal can be displaced. In one of the pair of insulators, a measurement pressure introduction hole for introducing a measurement pressure is formed, and in the other of the pair of insulators, a reference pressure introduction hole for introducing a reference pressure is formed, and An electrode is formed on at least one of the pair of insulators on the surface facing the diaphragm, and the displacement of the diaphragm due to the measurement pressure changes the capacitance between the diaphragm and the electrode. A pressure sensor chip for detecting from the pressure sensor case, a case in which the pressure sensor chip is housed, and a pressure introduction hole for introducing the measurement pressure is provided therein; A signal processing circuit that converts the capacitance of the sensor chip into a predetermined electric signal, wherein the case integrates a resin insulating part and a metal heat resistant part. The bottom case has a pressure-introducing hole provided in a heat-resistant portion of the bottom case, and the pressure sensor chip is disposed at a position deviated from the pressure-introducing hole, and the pressure sensor chip is disposed via a ceramic heat-resistant substrate. Fixed to the bottom case, between the heat-resistant portion of the bottom case and the heat-resistant substrate,
A capacitance-type pressure sensor, wherein a pressure introduction path extending from the pressure introduction hole to the pressure sensor chip is formed. 2. The capacitance type pressure sensor according to claim 1, wherein a material of an insulating portion of said bottom case is a thermoplastic resin. 3. The capacitance-type pressure sensor according to claim 2, wherein the thermoplastic resin forming the insulating portion of the case is made of a crystalline polymer. . 4. A capacitance type pressure sensor according to claim 1, wherein said bottom case is formed by previously placing a metal part to be said heat resistant part in a mold. A capacitance-type pressure sensor, wherein the insulating section and the heat-resistant section are integrally formed by insert molding. 5. A capacitance type pressure sensor according to claim 1, wherein said pressure sensor is used as a component of a gas meter. . 6. A capacitance type pressure sensor according to claim 1, wherein said pressure sensor chip is provided between a pair of conductive shield surfaces arranged in parallel with said electrode. And one of the pair of conductive shield surfaces is a metal film formed on the surface of the heat-resistant substrate, and the other is a metal plate supported by a supporting column erected on the substrate. A capacitance type pressure sensor characterized by the above-mentioned.