JP2004037225A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve accurate measurement by relaxing or intercepting the influence of heat from a pedestal in a relatively simple structure. <P>SOLUTION: A lead pin 4 is sealed into a case 2 by glass 3 for sealing. A recess 15 for positioning is formed at the center of the upper surface of the glass 3 for sealing, and a flow detection element 6 is installed in the recess 15 via the metal pedestal 5. A groove 17 for channels is formed on an upper surface of the pedestal 5 where the flow detection element 6 is joined. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas sensor for measuring and detecting the type, presence or absence, or flow rate of a gas, and more particularly to a mounting structure for a flow rate detection element.
[0002]
[Prior art]
For example, various types of thermal flow sensors for measuring the flow rate and flow velocity of a fluid have been conventionally proposed (eg, Japanese Patent Application Laid-Open Nos. 4-295724, 6-25684, and 8-146,026). Gazette).
[0003]
This type of flow sensor generally has a sensor formed by fixing a chip-shaped flow rate detecting element provided with a temperature detecting means to a fixing surface (upper surface) of a pedestal. It is installed and used horizontally. The reason for installing and using in a horizontal state is to prevent the generation of a vortex in the vicinity of the flow rate detecting element, which causes a decrease in measurement accuracy. That is, when a vortex is generated, the temperature distribution becomes non-uniform.
[0004]
As the material of the pedestal, a material having a small coefficient of thermal expansion, for example, glass, ceramics or the like is used. Further, in a sensor of a type in which a pedestal is sealed in a case by glass for sealing, a metal pedestal is used because a material having a melting point higher than that of glass for sealing is required. This also ensures horizontal installation of the flow detection element. As a material of the metal pedestal, Kovar (an alloy of 54% of Fe, 29% of Ni, and 17% of Co) having a thermal expansion coefficient close to that of glass or ceramics is usually used.
[0005]
As a method of attaching the flow rate detecting element to the fixing surface of the pedestal, the element is usually fixed closely to the fixing surface with an adhesive. At this time, if the adhesive adheres to the surface of the flow rate detecting element, the element becomes defective. In addition, if the temperature of the external environment changes irrespective of the quality of bonding, stress will be generated at the corners of the flow detection element due to the difference in the thermal expansion coefficient between the pedestal and the flow detection element. (Resistance value) changes.
[0006]
Therefore, as one method for solving such a problem, for example, the mounting structure described in Japanese Utility Model Laid-Open No. 5-18029 is used for preventing the adhesion of the adhesive, and for preventing the concentration of stress, for example, Japanese Patent Laid-Open No. An attachment structure described in Japanese Patent Application Laid-Open No. 5-103030 is known. That is, in the mounting structure described in Japanese Utility Model Laid-Open No. 5-18029, a protrusion is provided in a fixing area of a component such as a semiconductor bare chip, and an upper surface of the protrusion is used as a fixing surface of the component. The shape of the upper surface is made substantially the same as the fixing surface of the component, and the component is fixed to the upper surface of the projection with an adhesive. According to such a mounting structure, since the adhesive flowing out from between the projection and the component flows down along the side surface of the projection, there is an advantage that adhesion to the surface of the component can be prevented.
[0007]
On the other hand, in the mounting structure described in Japanese Utility Model Laid-Open No. 5-18030, a surface for fixing a component such as a semiconductor bare chip is formed so as to avoid a corner portion of the component, and the component is fixed to the fixing surface. Things. That is, the fixing surface is formed smaller than the component so that the corner of the component is not fixed to the fixing surface. According to such a mounting structure, when the temperature of the external environment changes, the stress generated in the component due to the difference in the thermal expansion coefficient is dispersed, and there is an advantage that the concentration of the stress on the corner portion can be prevented.
[0008]
[Problems to be solved by the invention]
As described above, conventionally, the fixing surface of the pedestal is formed as a flat surface that is substantially the same as or slightly smaller than the component, and the component is closely adhered to the fixing surface with an adhesive. However, such a mounting structure has a problem that the bonding area between the fixing surface and the component is large, so that it is easily affected by the heat from the pedestal, and high-precision measurement cannot be performed. That is, when the temperature of the pedestal changes in accordance with the temperature change of the external environment, the temperature of the flow rate detecting element also changes due to heat conduction and differs from the actual temperature of the fluid. As a result, the resistance value of the temperature detecting means changes the flow rate. This is because it changes with the temperature change of the element itself, and an error occurs in the flow measurement value. In particular, in the case of a flow sensor sealed with a sealing glass using a metal pedestal made of Kovar, the pedestal penetrates the sealing glass, and one end thereof protrudes outside the measurement flow path, and the temperature of the external environment is increased. The flow rate detection element is easily affected by temperature changes in the external environment through the pedestal, and when the fluid temperature changes, because the pedestal is directly affected by the change and the heat capacity and thermal conductivity of the pedestal are larger than those of glass, ceramics, etc. In addition, it takes time for the temperature of the flow detecting element and the base to become equal to the temperature of the fluid.
[0009]
Further, when the fluid hits the pedestal, the flow is disturbed and a vortex is generated in the vicinity of the flow rate detecting element, so that there is a problem that accurate measurement cannot be performed.
[0010]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to reduce or eliminate the thermal influence from the pedestal and prevent the generation of vortices with a relatively simple structure. To provide a gas sensor capable of performing highly accurate measurement.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention provides a metal case, a plurality of lead pins sealed in the case via sealing glass, and a plurality of lead pins disposed on an upper surface of the sealing glass. A pedestal, a temperature detecting element disposed on the pedestal, and a bonding wire connecting the temperature detecting element and the lead pin, wherein a lower surface of the element is in contact between the pedestal and the flow rate detecting element A channel or a gap is provided for measuring and detecting the type, presence or absence, or flow rate of gas.
In the first invention, since the pedestal is placed only on the windshield glass and does not protrude outside the measurement flow path, the pedestal is not directly subjected to the temperature change of the external environment, and the flow rate detecting element due to the temperature change of the external environment. Reduce thermal effects on
The flow channel grooves or voids reduce the contact area between the pedestal and the flow detection element and allow the fluid to contact the lower surface of the flow detection element. Therefore, the flow rate detecting element has little thermal influence from the pedestal, and quickly becomes equal to the temperature of the fluid even when the temperature of the fluid changes rapidly.
[0012]
According to a second aspect, in the first aspect, the pedestal is made of a metal having a small thermal expansion coefficient, and a gap is formed in a fixing surface to which the flow rate detecting element is fixed.
In the second aspect, the pedestal is made of metal having a small coefficient of thermal expansion, so that the pedestal has less thermal influence on the flow rate detecting element.
[0013]
According to a third aspect, in the first or second aspect, a positioning recess for positioning the pedestal is formed on an upper surface of the sealing glass.
In the third invention, the positioning recess positions the pedestal.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.
FIG. 1 is an external perspective view showing an embodiment in which the present invention is applied to a flow sensor, FIG. 2 is a cross-sectional view of the flow sensor, FIG. 3 is a perspective view of a flow detecting element and a pedestal, and FIG. It is sectional drawing of a pedestal.
[0015]
In these figures, a flow sensor indicated by a reference numeral 1 is composed of a case 2, a plurality of lead pins 4 sealed in the case 2 by a sealing glass 3, and a pedestal 5 on the upper surface of the sealing glass 3. It comprises a flow detecting element 6 installed via a bonding wire 7 for electrically connecting each of the lead pins 4 to the flow detecting element 6.
[0016]
The case 2 is formed of a metal having a small coefficient of thermal expansion, for example, Kovar or the like, into a cylindrical body whose both ends are open, and a flange 10 having an annular projection 9 is provided integrally on a base end outer peripheral surface. It is closely attached to the inner wall of the pipe 12 via a seal member 13 and is fixed by screws, an adhesive, welding, or the like. At the upper end of the case 2, an annular inner flange 14 bent inward at a substantially right angle is integrally provided.
[0017]
The sealing glass 3 is sealed over the entire inside of the case 2. In the center of the upper surface of the sealing glass 3, a positioning recess 15 having an appropriate depth for positioning the pedestal 5 is formed. The positioning recess 15 is formed by sealing the lead pin 4 with the sealing glass 3, solidifying the sealing glass 3, and then polishing the same, so that the bottom surface 15 a forms a flat surface perpendicular to the axis of the case 2. I have. As the sealing glass 3, for example, glass having a melting point of 1000 ° C. is used.
[0018]
The lead pin 4 is formed of Kovar or the like in the same manner as the case 2, has an upper end portion penetrating the sealing glass 3 and protruding above the case 2, a lower end portion also penetrating the sealing glass 3, and a pipe. It protrudes out of the twelve holes 16 and is connected to an external cord (not shown) via a connector.
[0019]
The pedestal 5 is formed of a metal having a thermal expansion coefficient close to that of glass or ceramics, specifically, Kovar, in the form of a small prism having substantially the same size as the flow rate detecting element 6. After being inserted and positioned, it is fixed by an adhesive. On the upper surface of the pedestal 5, a flow channel groove 17 for allowing the fluid 11 to flow and pass therethrough and four convex portions 18 are provided, and the upper surface 18a of these convex portions 18 is fixed to the flow rate detecting element 6. Forming a surface. That is, the flow rate detecting element 6 is fixed to the upper surface 18 a of the projection 18. The protrusions 18 are all protruded from the corners of the pedestal 5 at the same height, and the fixing surface 18 a is formed as a flat surface substantially perpendicular to the axis of the pedestal 5.
[0020]
The channel groove 17 has four openings 17a formed on the upper surface of the pedestal 5 and opened at the center of each side, and the unprocessed portion between the adjacent openings 17a forms the convex portion 18. Have been. Such channel grooves 17 and convex portions 18 can be easily formed by grinding.
[0021]
The flow channel groove 17 formed on the upper surface of the pedestal 5 is not limited to the groove having the four openings 17a shown in FIG. 3, but a straight line parallel to the flow direction of the fluid 11 as shown in FIG. Groove may be used. That is, in FIG. 5, the pedestal 5 is formed in the shape of a square chip, and a straight channel groove 17 which is open at the center of two sides of the four sides orthogonal to the flow direction of the fluid 11 is formed. The processing portion is a convex portion 18 facing in parallel with each other, and the flow rate detecting element is disposed thereon.
[0022]
The flow rate detecting element 6 has a silicon substrate 21 mounted on the fixing surface 18a of the pedestal 5 and fixed by an adhesive. The silicon substrate 21 is formed in a square chip shape having a side length of 23 mm and a thickness of about 0.5 mm, and has a diaphragm 24 having a large number of minute openings 23 in the center of the upper surface (indicated by a dotted line in FIG. 3). (A hexagonal part enclosed). A cavity 25 is formed below the diaphragm 24 by anisotropic etching. A sensor chip having such a cavity 25 is disclosed in Japanese Patent Publication No. 6-25684 and is conventionally known.
[0023]
On the upper surface of the diaphragm 24, one heating element (resistance heater) 31 and two temperature sensors 32A and 32B constituting the indirectly heated temperature detecting means 30 are formed by a known thin film forming technique. Further, a plurality of electrode pads 33 and a wiring metal thin film 34 are formed on the outer peripheral portion of the upper surface of the silicon substrate 21 at the same time when the heating element 31 and the temperature sensors 32A and 32B are formed by a thin film forming technique. For example, a material such as platinum is vapor-deposited on the surface of the electric insulating film formed on the surface of the silicon substrate 21 and etched by a predetermined pattern. Are electrically connected to each other through a metal thin film 34 for use. Each electrode pad 33 is electrically connected to the lead pin 4 via a bonding wire 7.
[0024]
The two temperature sensors 32 </ b> A and 32 </ b> B are arranged upstream and downstream of the fluid 11 with the heating element 31 interposed therebetween. The pattern width of the heating element 31 is 10 to 15 μm, and the pattern width of the temperature sensors 32A and 32B is 5 to 10 μm.
[0025]
The gas sensor 1 including such a flow detecting element 7 is mounted in a pipe 12 such that the upper surface of the flow detecting element 6 is parallel to the flow direction of the fluid 11 (the direction of the arrow). In addition, when mounting, the flow channel groove 17 is mounted so as to coincide with the flow direction of the fluid 11 so as not to disturb the flow of the fluid 11. In the case of the flow channel groove 17 having four openings 17a shown in FIG. 3, it is desirable to mount the inside of the pipe 12 so that the two openings 17a facing each other are parallel to the flow direction of the fluid 11. .
[0026]
In the flow sensor 1 having such a structure, if the fluid 11 is caused to flow in the direction of the arrow in FIG. 3 while the heating element 31 is heated to a certain higher temperature than the ambient temperature by energization, the upstream temperature of the heating element 31 Since a temperature difference occurs between the sensor 32A and the downstream temperature sensor 32B, the flow rate or the flow rate of the fluid 11 can be measured by detecting the voltage difference or the resistance value difference by a bridge circuit as shown in FIG. it can.
[0027]
Here, the circuit shown in FIG. 6 supplies a voltage output using a bridge circuit including two temperature sensors 32A and 32B. In this case, since the two temperature sensors 32A and 32B are used, there is an advantage that the flow direction of the fluid 11 can be detected. That is, since the fluid 11 is warmed by the heating element 31, a temperature difference occurs between the temperature sensor 32A located on the upstream side of the heating element 31 and the temperature sensor 32b located on the downstream side, whereby the flow direction of the fluid 11 is determined. Is done. R1 and R2 are resistors, and OP is an operational amplifier.
[0028]
According to the flow sensor 1 having the above-described structure, since the flow channel groove 17 is formed on the upper surface of the metal pedestal 5, the contact area between the pedestal 5 and the flow rate detecting element 6 can be reduced. Therefore, the influence of the temperature of the pedestal 5 can be reduced. Further, since the pedestal 5 is installed on the upper surface of the sealing glass 3 and does not protrude outside the pipe 12, the temperature of the pedestal 5 does not directly change due to the temperature of the external environment, and the heat to the flow rate detecting element 6 is not changed. Impact can be reduced. Therefore, highly accurate flow measurement can be performed. Also, since the flow rate detecting element 6 is in contact with the fluid 11 not only on the upper surface but also on the lower surface, even when the temperature of the fluid 11 changes suddenly, the temperature of the fluid 11 immediately becomes equal to the temperature of the fluid 11, and More accurate measurement can be performed.
[0029]
FIG. 7 is a perspective view showing an embodiment in which the present invention is applied to a hydrogen gas sensor.
In the figure, a hydrogen gas sensor 40 includes a catalytic metal film 42 provided on the surface of a substrate 41 and a thermoelectric conversion material film 43, and these films 42, 43 are connected to lead pins 4, 4 via bonding wires 7, respectively. are doing. The catalyst metal film 42 is formed by a sputtering method using a platinum catalyst film as a material that causes a catalytic reaction with hydrogen gas. The thermoelectric conversion material is a material that converts a temperature gradient into a voltage by the Bebeck effect. For example, nickel oxide to which lithium is added is used, and the thermoelectric conversion material film 43 is formed by a screen printing method.
[0030]
The substrate 41 is mounted on the pedestal 5, and a gap 44 is formed on a joint surface of the pedestal 5 with the substrate 41 to prevent external heat transfer. 2 is a case, 3 is sealing glass.
[0031]
In the hydrogen gas sensor 40 having such a structure, when hydrogen gas comes into contact with the platinum catalyst film 42, a catalytic reaction occurs and the platinum catalyst film 42 generates heat. Hydrogen gas can be detected by converting a local temperature difference generated by the heat generation into a voltage signal by the thermoelectric conversion material film 43. Further, as the hydrogen gas concentration increases, the voltage signal also increases, so that it is also used as a hydrogen concentration sensor.
[0032]
In the embodiment shown in FIG. 1, the spatial temperature distribution of the fluid 11 due to the heat generated from the heat generating element 31 causes a bias due to the flow, and the indirectly heated type is detected by the temperature sensors 32A and 32B. Although the sensor is shown, the invention is not limited thereto, and a self-heating type sensor that detects a change in electric power or a change in resistance due to deprivation of heat of the heating element 31 by the fluid 11 and detects a flow rate or a flow velocity may be used. . The number of temperature sensors is not limited to two, but may be one. In short, the flow rate detecting element 6 may be anything that can measure the flow rate or the flow velocity.
Further, in the above-described embodiment, an example in which the positioning concave portion 15 is formed on the upper surface of the sealing glass 3 is shown. However, this is not always necessary, and the entire upper surface is formed into a flat surface by polishing. The flow rate detecting element 6 may be joined thereon.
Further, the pedestal 5 and the flow rate detecting element 6 are not limited to the square shape, but may be formed in a circular shape.
[0033]
【The invention's effect】
As described above, according to the gas sensor according to the present invention, the thermal influence from the pedestal on the flow rate detecting element can be reduced by forming the flow channel or the gap, so that the measurement accuracy can be improved.
Also, when used in a flow sensor, the flow rate detection element increases the contact area with the fluid due to the formation of the flow channel groove, so it can respond to instantaneous changes in the temperature of the fluid and perform more accurate measurement. Can be.
[Brief description of the drawings]
FIG. 1 is an external perspective view showing an embodiment of a gas sensor according to the present invention.
FIG. 2 is a sectional view of the gas sensor.
FIG. 3 is a perspective view of a flow detecting element and a base.
FIG. 4 is a cross-sectional view of a flow rate detection element and a pedestal.
FIG. 5 is a perspective view showing another embodiment of the channel groove.
FIG. 6 is an electric circuit diagram of a flow detection element.
FIG. 7 is a perspective view showing an embodiment in which the present invention is applied to a hydrogen gas sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 2 ... Case, 3 ... Sealing glass, 4 ... Lead pin, 5 ... Pedestal, 6 ... Flow detecting element, 7 ... Bonding wire, 11 ... Fluid, 15 ... Positioning recess, 17 ... Channel groove, 18: convex portion, 21: silicon substrate, 30: temperature detecting means, 31: heating element, 32A, 32B: temperature sensor, 40: hydrogen gas sensor.

Claims (3)

A metal case, a plurality of lead pins sealed in the case via sealing glass, a pedestal disposed on the upper surface of the sealing glass, and a temperature disposed on the pedestal. A detecting element, and a bonding wire connecting the temperature detecting element and the lead pin;
A gas sensor, characterized in that a flow channel groove or a gap where the lower surface of the element is in contact is provided between the pedestal and the flow rate detection element, and the type, presence or absence, or flow rate of gas is measured and detected. The gas sensor according to claim 1,
A gas sensor, wherein the pedestal is made of metal having a small coefficient of thermal expansion, and a gap is formed in a fixing surface to which the flow rate detecting element is fixed. The gas sensor according to claim 1, wherein
A gas sensor, wherein a positioning recess for positioning the pedestal is formed on an upper surface of the sealing glass.

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