JP2002318149A - Flow sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable measurement with high accuracy by relaxing or blocking influence of heat from a pedestal with a relatively simple structure. SOLUTION: A pedestal 4 made of metal and a lead pin 5 are sealed in a case 3 with a sealing glass 2, and a flow rate detecting element 7 is mounted on an upper face of the pedestal 4. A groove 30 for passage is formed on a lower face of the flow rate detecting element 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow sensor for measuring a flow rate or a flow rate of a fluid, and more particularly to a mounting structure for a flow rate detecting element.

[0002]

2. Description of the Related Art Various types of thermal type flow sensors for measuring a flow rate and a flow velocity of a fluid have been conventionally proposed (for example:
JP-A-4-295724, JP-B-6-25684
JP-A-8-14626 and the like.

[0003] This type of flow sensor generally comprises a sensor in which a chip-shaped flow detecting element provided with a temperature detecting means is fixed to a fixing surface of a pedestal. It is installed and used horizontally. The installation and use in a horizontal state is to prevent vortices from being generated in the vicinity of the flow rate detecting element (measured accuracy is reduced by turbulence in temperature distribution when vortices are generated).

As a 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 with sealing glass, a metal pedestal is used because a material having a higher melting point than that of the sealing glass is required. This also ensures horizontal installation of the flow detection element. As a material for the metal pedestal, Kovar (Fe54) having a thermal expansion coefficient close to that of glass or ceramics is used.
%, Ni 29%, and Co 17% alloy) are usually used.

As a method of attaching the flow rate detecting element to the fixing surface of the pedestal, the element is usually closely attached to the fixing surface and fixed by 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 regardless of the bonding quality, 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. Deteriorates.

Therefore, as one of the methods for solving such a problem, for preventing the adhesion of the adhesive, for example, a mounting structure described in Japanese Utility Model Laid-Open No. 5-18029 is disclosed.
Regarding the prevention of stress concentration, see, for example,
A mounting structure described in Japanese Patent Publication No. 30 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, and a protrusion of the protrusion is formed. The shape of the upper surface is 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.

On the other hand, in the mounting structure described in Japanese Utility Model Application 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. It is like that. 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, there is an advantage that 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 the concentration of the stress on the corner portion can be prevented.

[0008]

As described above, conventionally, the fixing surface of the pedestal is formed as a flat surface which is substantially the same as or slightly smaller than the component, and the component is closely adhered to the fixing surface with an adhesive. I was However, with such a mounting structure,
Since the bonding area between the fixed surface and the component is large, there is a problem in that it is easily affected by the heat from the pedestal, and high-precision measurement cannot be performed. In other words, 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 detection value. It may change with the temperature change of the element itself, causing an error in the flow measurement value.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has as its object to alleviate or block the influence of heat from a pedestal with a relatively simple structure.
It is an object of the present invention to provide a flow sensor that enables highly accurate measurement.

[0010]

According to a first aspect of the present invention, there is provided a flow rate detecting element provided with temperature detecting means for detecting a temperature of a fluid, and a pedestal on which the flow rate detecting element is mounted. Wherein a flow channel groove is provided on the lower surface of the flow rate detecting element along the flow direction of the fluid.

According to a second aspect, in the first aspect,
The substrate of the flow rate detecting element is made of silicon, and the channel groove is formed by etching.

In the present invention, the contact area between the pedestal and the flow rate detecting element is reduced in the channel groove. Therefore, even if the temperature of the pedestal changes due to a change in the temperature of the external environment, the thermal effect on the flow rate detecting element can be reduced. In addition, since the lower surface of the flow rate detecting element comes into contact with the fluid by forming the channel groove, it can cope with an instantaneous temperature change. Since the channel groove can be formed in the silicon etching process,
The flow detection element can be manufactured at low cost.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 of a flow sensor according to the present invention, FIG. 2 is a cross-sectional view of the flow sensor, FIG. 3 is an enlarged perspective view showing a flow detecting element, and FIG. It is sectional drawing of an element.

In these figures, a flow sensor indicated generally by reference numeral 1 is a metal pedestal 4 and a plurality of lead pins 5 sealed in a case 3 by a sealing glass 2.
And a flow rate detecting element 7 fixed to the upper surface of the pedestal 4 and the like.

The case 3 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 with a projection 9 is integrally provided on the outer peripheral surface of the base end. Is closely attached to the inner wall of a pipe 12 through which the fluid 11 flows through a seal member 13 and is fixed by screws, an adhesive, welding, or the like.

The pedestal 4 is formed of a metal having a thermal expansion coefficient close to that of glass or ceramics, specifically, a long and narrow rectangular bar made of Kovar, and is disposed at the center of the case 3 so that the axes thereof substantially coincide with each other. It penetrates through the sealing glass 2 and protrudes above the case 3, and the lower end also penetrates through the sealing glass 2 and protrudes below the case 3, and further through the hole 14 provided in the pipe 12 to the outside of the pipe 12. It is protruding. The upper surface 4a of the pedestal 4 is substantially the same size as the flow rate detecting element 7 and is formed on a flat surface substantially perpendicular to the axis of the pedestal 4 to form a fixing surface of the flow rate detecting element 7.

The lead pin 5 is also provided through the sealing glass 2, the upper end is electrically connected to the flow detecting element 7 by a bonding wire 15, and the lower end protrudes outside the pipe 12.

The flow rate detecting element 7 has a silicon substrate 20 mounted on the fixing surface 4a of the pedestal 4 and fixed by an adhesive. The silicon substrate 20 is formed in a square chip shape having a side length of about 1.7 mm and a thickness of about 0.5 mm, and has a diaphragm 27 having a large number of openings 21a at the center of the upper surface (dotted line in FIG. 1). (A hexagonal portion surrounded by a circle). Below the diaphragm 27,
The space 18 is formed by anisotropic etching, and allows the fluid 11 to flow through the opening 27a. Note that a sensor chip having such a space portion 18 is disclosed in Japanese Patent Publication No. 6-25684 and is conventionally known.

On the upper surface of the diaphragm, one heating element (resistance heater) constituting the indirectly heated temperature detecting means 22 is provided.
23 and two temperature sensors 24A and 24B are formed by a known thin film forming technique. Further, a plurality of electrode pads 26 and a metal thin film 27 for wiring are formed on the outer peripheral portion of the upper surface of the silicon substrate 20 by the thin film forming technique.
It is formed simultaneously with the formation of the temperature sensors 24A and 24B. 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 20 and is etched by a predetermined pattern, and the heating element 23 and the temperature sensors 24A and 24B are wired to the electrode pads 26 Are electrically connected via the metal thin film 27 for use. Each electrode pad 26 is electrically connected to the lead pin 5 via a bonding wire 15.

The two temperature sensors 24A and 24B are
They are arranged upstream and downstream of the fluid 11 with the heating element 23 interposed therebetween. The pattern width of the heating element 23 is 10 to 1
5 μm, the pattern width of the temperature sensors 24A and 24B is 5
10 μm.

Further, on the back surface of the silicon substrate 20, a flow channel groove 3 for allowing the fluid 11 to flow and pass therethrough.
0 is formed by etching, and the unprocessed portion forms a fixed portion 31 with the pedestal 4.

The channel groove 30 is formed as a cross-shaped groove that is open at the center of each side while leaving the four corners of the back surface of the silicon substrate 20 as unprocessed portions. Constitute the thick fixing portion 31. Such a channel groove 30 can be easily formed by etching when the diaphragm 21 is formed, but is not limited to this, and may be formed by grinding.

The channel groove 30 formed in the silicon substrate 20 is not limited to the cross-shaped groove shown in FIGS. 3 and 4, but may be formed as shown in FIGS. 5 (a) and 5 (b). Channel grooves 32 and 33 may be used. That is, FIG.
Is a groove formed so as to open to the center of two sides orthogonal to the flow direction of the fluid 11 among the four sides of the silicon substrate 20, and the flow path groove shown in FIG. The use groove 33 is a groove formed so as to open in a diagonal direction orthogonal to the flow direction of the fluid 11.

The flow sensor 1 having such a flow detecting element 7 is mounted in a pipe 12 such that the upper surface of the flow detecting element 7 is parallel to the flow direction of the fluid 11 (the direction of the arrow). At the time of mounting, the flow grooves 30, 32, or 33 are provided with the fluid 11 so as not to disturb the flow of the fluid 11.
Install so that it matches the flow direction. 3 and 4
In the case of the cross-shaped flow channel groove 30 shown in FIG. 1, one of the two diagonal lines of the flow rate detecting element 7 is parallel to the flow direction of the fluid 11, in other words, the flow channel groove 30 is It is desirable to be mounted in the pipe 12 so as to intersect at an angle of about 45 ° with the flow direction of the pipe 11.

In the flow sensor 1 having such a structure, when the heating element 23 is heated to a certain higher temperature than the ambient temperature by energization, the fluid 11 flows in the direction of the arrow in FIG. Since a temperature difference occurs between the upstream temperature sensor 24A and the downstream temperature sensor 24B, the flow rate or the flow rate of the fluid 11 is measured by detecting the voltage difference or the resistance value difference by a bridge circuit as shown in FIG. I do.

The circuit shown in FIG. 6 supplies a voltage output using a bridge circuit including two temperature sensors 24A and 24B. In this case, two temperature sensors 2
Since 4A and 24B are used, there is an advantage that the direction of the flow of the fluid 11 can be detected. In addition, R1, R2
Is a resistor, and OP is an operational amplifier.

According to the flow sensor 1 having the above structure, the flow channel groove 30 (32, 3
Since 3) is formed and the fixing portion 31 is joined to the pedestal 4, the contact area between the pedestal 4 and the flow rate detecting element 7 can be reduced. Therefore, even if the temperature of the pedestal 4 changes due to a change in the temperature of the external environment, the thermal effect on the flow rate detecting element 7 can be reduced, and highly accurate flow rate measurement can be performed. In addition, since not only the upper surface but also the lower surface of the flow detecting element 7 is in contact with the fluid 11, even when the temperature of the fluid 11 changes rapidly, it changes following the temperature and quickly becomes equal to the temperature of the fluid 11. Therefore, more accurate measurement can be performed.

In the above-described embodiment, the spatial temperature distribution of the fluid 11 due to the heat generated from the heating element 23 is deviated by the flow, and this is detected by the temperature sensor 24.
Although the indirectly heated sensor detected by A and 24B is shown, the invention is not limited to this, and a change in electric power or a change in resistance due to deprivation of heat of the heating element 23 by the fluid 11 is detected to detect a flow rate or a flow velocity. A self-heating type sensor may be used. The number of temperature sensors is not limited to two, but may be one.

In the above-described embodiment, silicon is used as the substrate material of the flow rate detecting element 7. However, the present invention is not limited to this, and various materials can be used. For example, it is possible to use stainless steel having low thermal conductivity and high heat resistance, corrosion resistance and rigidity, and to cover the entire surface with an electric insulating film, or use sapphire, alumina ceramics, or the like.

[0030]

As described above, according to the present invention, the thermal influence of the pedestal on the flow rate detecting element can be reduced, so that the measurement accuracy can be improved. Also, since the contact area between the flow detection element and the fluid increases,
It can respond to an instantaneous change in the temperature of the fluid, and can perform more accurate measurement.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing an embodiment of a flow sensor according to the present invention.

FIG. 2 is a sectional view of the flow sensor.

FIG. 3 is a perspective view of a flow detection element.

FIG. 4 is a sectional view of the flow rate detecting element.

FIGS. 5A and 5B are perspective views of a flow rate detecting element showing another embodiment of the flow channel groove, respectively.

FIG. 6 is an electric circuit diagram of a flow detection element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flow sensor, 2 ... Glass for sealing, 3 ... Case, 4
... pedestal, 5 ... lead pin, 7 ... flow rate detecting element, 11 ... fluid, 22 ... temperature detecting means, 30, 32, 33 ... flow path groove.

Claims (2)

[Claims] 1. A flow sensor comprising a flow detecting element provided with temperature detecting means for detecting a temperature of a fluid, and a pedestal on which the flow detecting element is mounted. A flow sensor, wherein a groove is provided along a flow direction of the fluid. 2. The flow sensor according to claim 1, wherein the substrate of the flow rate detecting element is made of silicon and the groove for the flow path is formed by etching.