JP3740027B2 - Flow sensor - Google Patents

Description

[0001]
BACKGROUND 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 detection element.
[0002]
[Prior art]
Various types of thermal flow sensors for measuring the flow rate and flow velocity of fluids have been proposed in the past (eg, Japanese Patent Laid-Open No. 4-295724, Japanese Patent Publication No. 6-25684, Japanese Patent Laid-Open No. 8-146026, etc.) ).
[0003]
This type of flow sensor is generally configured by fixing a chip-shaped flow rate detection element equipped with a temperature detection means to the fixing surface (upper surface) of the pedestal. Installed and used horizontally. The installation is used in a horizontal state in order to prevent a vortex from being generated in the vicinity of the flow rate detecting element (when the vortex is generated, the measurement accuracy decreases).
[0004]
As a material for the pedestal, a metal pedestal is used because a sensor having a melting point higher than that of the sealing glass is required in a sensor of a type in which the pedestal is sealed with sealing glass in the case. This also ensures a horizontal installation of the flow rate detecting element. As a material for the metal pedestal, Kovar (alloy of 54% Fe, 29% Ni, 17% Co) having a thermal expansion coefficient close to that of glass or ceramic 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 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 regardless of whether the adhesive is good or bad, stress is generated at the corners of the flow rate detection element due to the difference in the thermal expansion coefficient between the pedestal and the flow rate detection element. The electrical characteristics of the are deteriorated.
[0006]
Therefore, as one method for solving such a problem, the attachment structure described in, for example, Japanese Utility Model Laid-Open No. 5-18029 is used for preventing adhesion of an adhesive, and for example, the practical use of Japanese Unexamined A mounting structure described in Japanese Patent Laid-Open No. 5-18030 is known. That is, in the mounting structure described in Japanese Utility Model Publication No. 5-18029, a protrusion is provided in a fixing area of a component such as a semiconductor bare chip, and the 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 protrusion with an adhesive. According to such an attachment structure, since the adhesive flowing out between the protrusion and the part flows down along the side surface of the protrusion, there is an advantage that adhesion to the surface of the part can be prevented.
[0007]
On the other hand, in the mounting structure described in the Japanese Utility Model Laid-Open No. 5-18030, the fixing surface with a component such as a semiconductor bare chip is formed so as to avoid the corner portion of the component, and the component is fixed to the fixing surface. Is. That is, the fixing surface is formed to be smaller than the component so that the corner portion 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 thermal expansion coefficient is dispersed, and there is an advantage that stress concentration at 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 on a flat surface substantially the same as or slightly smaller than the component, and the component is in close contact with the fixing surface and fixed with an adhesive. However, such a mounting structure has a problem in that since the bonding area between the fixing surface and the part is large, it is easily affected by heat from the pedestal and high-precision measurement cannot be performed. That is, if the temperature of the pedestal changes with the temperature change of the external environment, the temperature of the flow rate detection element also changes due to heat conduction, which differs from the actual temperature of the fluid, and as a result, the resistance value of the temperature detection means detects the flow rate. This is because the temperature changes with the temperature of the element itself and an error occurs in the flow rate measurement value. In particular, in the case of a flow sensor that uses a metal base made of Kovar and is sealed with sealing glass, the heat capacity and thermal conductivity of the base are larger than those of glass, ceramics, etc. It takes time for the temperature of the flow rate detecting element and the pedestal to become equal to the temperature of the fluid when the temperature of the fluid changes easily.
[0009]
In addition, when the fluid hits the pedestal, the flow is disturbed and a vortex is generated in the vicinity of the flow rate detecting element, which makes it impossible to perform accurate measurement.
[0010]
The present invention has been made to solve the above-described conventional problems. The object of the present invention is to reduce or block the thermal influence from the pedestal and prevent the generation of vortices with a relatively simple structure. An object of the present invention is to provide a flow sensor that can perform measurement with high accuracy.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first invention provides a flow rate detecting element provided with temperature detecting means for detecting the temperature of a fluid, a pedestal on which the flow rate detecting element is mounted, and sealing the pedestal in a case. In the flow sensor provided with the sealing glass, the pedestal is formed of glass, ceramics or the like having a melting point higher than that of the sealing glass, and an upper end portion of the pedestal is protruded from the sealing glass and the flow rate on the upper surface. The detection element is fixed.
In the first invention, the pedestal formed of glass or ceramics has a smaller heat capacity and thermal conductivity than Kovar, and reduces the thermal influence on the flow rate detection element from the pedestal due to temperature changes in the external environment. When the temperature of the fluid changes, the temperature of the pedestal also changes and quickly becomes equal to the temperature of the fluid.
[0012]
According to a second invention, in the first invention, a channel groove is formed along the fluid flow direction on the upper surface of the pedestal where the flow rate detecting element is fixed.
In the second aspect of the present invention, the flow path groove reduces fluid disturbance due to the pedestal as the fluid passes through. Therefore, the generation of vortices is small. Further, the contact area between the pedestal and the flow rate detection element is reduced, and the contact area between the flow rate detection element and the fluid is increased.
[0013]
According to a third invention, in the first or second invention, the lower end of the pedestal is located in the sealing glass and does not protrude to the outside.
In 3rd invention, since the lower end part is located in the glass for sealing, a base is hard to receive the temperature change of an external environment.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments 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 sectional view of the flow sensor, and FIG. 3 is a perspective view of a flow rate detecting element and a pedestal.
[0015]
In these drawings, a flow sensor generally indicated by reference numeral 1 includes a plurality of lead pins 4 and a pedestal 5 sealed in a case 2 by a sealing glass 3, and an upper surface protruding from the sealing glass 3 of the pedestal 5. The flow rate detecting element 6 and the like are fixed to each other.
[0016]
The case 2 is formed in a cylindrical body whose both ends are opened by a metal having a small coefficient of thermal expansion, such as Kovar, and a flange 10 with protrusions 9 is integrally provided on the outer peripheral surface of the base end portion. 11 is in close contact with the inner wall of the pipe 12 through which the pipe 11 flows, and is fixed by screws, an adhesive, welding, or the like.
[0017]
The sealing glass 3 is sealed over the entire inside of the case 2. 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, the upper end portion projects through the sealing glass 3 and protrudes upward from the case 2, the lower end portion penetrates the sealing glass 3, and the pipe 12. It protrudes outside from the hole 14 and is connected to an external cord (not shown).
[0019]
The pedestal 5 is substantially the same as the flow rate detecting element 6 by a material (for example, glass ceramics having a melting point of 2000 ° C.) having a smaller heat capacity and thermal conductivity than Kovar and having a melting point higher than that of the sealing glass 3. It is formed in a small prismatic shape (or chip shape) having a size, and a lower end portion is sealed to the sealing glass 3 so as to be positioned on the center line of the case 2, and an upper end portion is located above the sealing glass 3. It protrudes. Further, the upper surface of the pedestal 5 is provided with a channel groove 15 and four convex portions 16, and the upper surface of these convex portions 16 forms a fixing surface 16 a of the flow rate detecting element 6. That is, the flow rate detection element 6 is fixed to the upper surface of the convex portion 16. The convex portions 16 are all the same height, and the fixing surface 16 a is formed on a flat surface substantially perpendicular to the axis of the pedestal 5.
[0020]
The flow channel groove 15 is formed in a cross shape so as to open to the center of the four sides of the pedestal 5, and the portions other than the groove portion constitute the convex portion 16, and are formed at the four corners on the upper surface of the pedestal 5, respectively. positioned.
[0021]
The channel grooves formed on the surface of the pedestal 5 are not limited to the cross-shaped passage grooves 15 shown in FIG. 3, but are linearly formed diagonally on the upper surface of the pedestal 5 as shown in FIG. The passage groove 20 may be used. That is, the linear flow channel groove 20 shown in FIG. 4 is a groove formed so as to open to one diagonal line of the pedestal 5, and is a diagonal line perpendicular to the flow direction of the fluid 11. The unprocessed portions made of triangular prisms are left, and these unprocessed portions serve as the convex portions 21 on which the flow rate detecting element 6 is installed.
[0022]
Such a pedestal 5 has a side length L of about 1.5 mm and a height H of about 1-2 mm, which is lower than the height of the case 2 (about 3.6 mm). The height (= depth of the channel groove 15) H1 of the convex portion 16 is about 0.7 mm, and the length L1 of one side of the convex portion 16 is about 0.3 mm.
[0023]
It is possible to manufacture the pedestal 5 one by one. However, since the processing of the groove 15 (20) for the passage is troublesome and the manufacturing cost is high, one large material is manufactured for manufacturing the semiconductor chip. It is preferable to form a plurality of pedestals 5 at the same time by dicing small like the above.
[0024]
In FIG. 3, the flow rate detecting element 6 has a silicon substrate 31 that is placed on the pedestal 5 and fixed by an adhesive. The silicon substrate 31 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 a diaphragm 32 is formed by thinning the central portion by etching the central portion of the lower surface. Further, on the upper surface of the diaphragm 32, one heating element (resistive heater) 34 and two temperature sensors 35A, 35B constituting the indirectly heated type temperature detecting means 33 are formed by a well-known thin film forming technique. . Further, a plurality of electrode pads 36 and a wiring metal thin film 37 are formed on the outer peripheral portion of the upper surface of the silicon substrate 31 simultaneously with the formation of the heating element 34 and the temperature sensors 35A and 35B by a thin film forming technique. For example, a material such as platinum is deposited on the surface of the electrical insulating film formed on the surface of the silicon substrate 31 and etched into a predetermined pattern. The heating element 34 and the temperature sensors 35A and 35B are wired to the electrode pad 36. The metal thin films 37 are electrically connected to each other. Each electrode pad 36 is electrically connected to the lead pin 4 through a bonding wire 38 (FIG. 2).
[0025]
The two temperature sensors 35A and 35B are arranged on the upstream side and the downstream side of the fluid 11 with the heating element 34 interposed therebetween. The pattern width of the heating element 34 is 10 to 15 μm, and the pattern width of the temperature sensors 35A and 35B is 5 to 10 μm.
[0026]
The flow sensor 1 having such a flow rate detection element 6 is attached in the pipe 12 so that the upper surface of the flow rate detection element 6 is parallel to the flow direction (arrow direction) of the fluid 11. In addition, in order to prevent the flow of the fluid 11 from being disturbed, the flow path groove 15 (or 20) is attached so as to coincide with the flow direction of the fluid 11. In the case of the cross-shaped channel groove 15 shown in FIG. 3, one of the two diagonal lines of the flow rate detection element 6 is parallel to the flow direction of the fluid 11, in other words, the channel groove. It is desirable to install in the pipe 12 so that 15 intersects with the flow direction of the fluid 11 at an angle of about 45 °.
[0027]
In the flow sensor 1 having such a structure, when the fluid 11 is flowed in the direction of the arrow in FIG. 3 while the heating element 34 is heated to a certain higher temperature than the ambient temperature by energization, the upstream temperature of the heating element 34 is increased. Since a temperature difference is generated between the sensor 35A and the downstream temperature sensor 35B, the flow rate or flow rate of the fluid 11 is measured by detecting the voltage difference or resistance value difference using a bridge circuit as shown in FIG.
[0028]
Here, the circuit shown in FIG. 5 supplies a voltage output using a bridge circuit including two temperature sensors 35A and 35B. In this case, since the two temperature sensors 35A and 35B are used, the flow direction of the fluid 11 can also be detected by the temperature difference. R1 and R2 are resistors, and OP is an operational amplifier.
[0029]
FIG. 6 shows a manufacturing procedure of the flow sensor 1 having the above structure.
The flow sensor 1 is manufactured using a firing jig 60 shown in FIG. The firing jig 60 includes a first jig 61 having a large number of holes 62 into which the case 2 can be fitted, a second jig 63 having a large number of pin holes 64 through which the lead pins 4 pass, and a pedestal. And a third jig 65 having a large number of holes 66 into which the upper end portions of 5 can be fitted.
[0030]
First, the lead pin 4 is inserted into the pin hole 64 of the second jig, the first jig 61 is positioned and placed on the second jig 63, and the upper end portion of each lead pin 4 is placed on the second jig 63. 1 is positioned in the hole 2 of the jig 61 (FIG. 6B). Next, the sealing glass body 67 is fitted into the hole 62 of the first jig 61, and the upper end portion of the lead pin 4 is inserted into the insertion hole provided in the sealing glass body 67. The glass body 67 for sealing is formed into a shape of a required size by molding powder glass with a press and pre-baking (FIG. 6C).
[0031]
Next, the case 2 is inserted into the hole 62 of the first jig and fitted into the sealing glass body 67 (FIG. 6D). Next, the upper end portion of the base 5 is fitted into the hole 66 of the third jig 65 so that the lower end portion protrudes downward. And the 3rd jig | tool 65 is positioned and overlapped on the 1st jig | tool 61, and the lower end part of the base 5 is inserted in the hole 68 provided in the center of the sealing glass body 67 (FIG.6 (e)). ).
[0032]
Next, the superimposed first, second, and third jigs 61, 63, and 65 are placed in a firing furnace, and the sealing glass body 67 is fixed at a temperature lower than the melting point of the base 5 (eg, about 1000 ° C.) for a certain period of time. By melting by heating, the sealing glass 3 shown in FIG. 2 is obtained, and the lead pins 4 and the pedestal 5 are sealed in the case 2. At this time, since the pedestal 5 is formed of a material having a melting point higher than that of the sealing glass 3, there is no possibility that the shape changes due to softening or melting. Thereafter, when the firing jig 60 is removed from the firing furnace and the first, second, and third jigs 61, 63, 65 are separated, the lead pin 4 and the base 5 are sealed in the case 2 by the sealing glass 3. A worn semi-finished product is obtained.
[0033]
Next, the flow rate detecting element 6 is placed on the fixing surface 16a of the convex portion 16 of the base 5 and fixed with a bonding agent, and the lead pin 4 and the electrode pad 36 of the flow rate detecting element 6 are electrically connected by a bonding wire 38. Thus, the production of the flow sensor 1 is finished.
[0034]
In the flow sensor 1 having the above structure, the pedestal 5 is formed of glass, ceramics, or the like having a higher melting point than the sealing glass 3, and the case 2 and the pedestal 5 are sealed by the sealing glass 3. Compared to a metal pedestal, the heat capacity and thermal conductivity are small. Even if the temperature of the external environment changes, the temperature change of the pedestal 5 is small, and the thermal influence on the flow rate detecting element 6 can be reduced. In addition, the pedestal 5 has an upper end protruding above the case 2 and positioned in the fluid 11, and a lower end positioned in the sealing glass 3 and does not protrude outside the pipe 12. It is difficult to receive, and the thermal influence on the flow rate detecting element 6 is further reduced or blocked. Therefore, when the temperature of the fluid 11 changes, the temperature of the pedestal 5 also changes quickly and becomes equal to the temperature of the fluid. In addition, since the flow rate detecting element 6 is in contact with the fluid 11 not only at the upper surface but also at the lower surface, the contact area with the fluid 11 is large and the temperature equal to the temperature of the fluid 11 is maintained. Furthermore, since the pedestal 5 has a channel groove 15 (20) through which the fluid 11 flows in and passes, the pedestal 5 does not disturb the flow of the fluid 11 or generate a vortex. Highly accurate measurement can be performed.
[0035]
In the embodiment described above, an indirectly heated sensor is shown in which the spatial temperature distribution of the fluid 11 caused by the heat from the heating element 34 is biased by the flow, and this is detected by the temperature sensors 35A and 35B. However, the present invention is not limited to this, and a self-heating type sensor that detects a change in electric power or a change in resistance due to the heat 11 deprived of heat by the fluid 11 and detects a flow rate or a flow rate may be used. Further, the number of temperature sensors is not limited to two, and may be one. In short, the flow rate detecting element 7 may be any device as long as it can measure the flow rate or the flow velocity.
[0036]
Further, in the above-described embodiment, an example in which the pedestal 5 is formed in a prismatic shape has been shown.
[0037]
【The invention's effect】
As described above, the flow sensor according to the present invention can satisfactorily seal a pedestal made of glass, ceramic or the like with sealing glass in the case, and the pedestal has a heat capacity and heat conduction compared to a metal pedestal. Since the rate is small, the thermal influence on the flow rate detection element due to an external temperature change can be reduced, and the measurement accuracy can be improved.
[0038]
Further, in the invention in which the channel groove is provided on the surface on which the flow rate detection element of the pedestal is installed, the contact area between the pedestal and the flow rate detection element is small, and the contact area between the flow rate detection element and the fluid is increased. Even when the temperature of the fluid changes abruptly, the temperature of the flow rate detecting element changes following the temperature of the fluid, and can be quickly made equal to the temperature of the fluid. In addition, the flow channel groove reduces the disturbance of the fluid flow caused by the pedestal, so there is no vortex around the flow rate detection element, making it possible to perform more accurate measurements and improving the measurement accuracy of the flow sensor. Can be made.
[0039]
Furthermore, in the invention configured such that the lower end portion of the pedestal is positioned in the sealing glass and is not protruded to the outside, since the external temperature change is not directly received, the thermal influence on the flow rate detecting element is further reduced or reduced. be able to.
[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 rate detecting element and a pedestal.
FIG. 4 is a perspective view showing another embodiment of a pedestal.
FIG. 5 is an electric circuit diagram of a flow rate detection element.
FIGS. 6A to 6E are diagrams for explaining a flow sensor manufacturing procedure; FIGS.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Flow sensor, 2 ... Case, 3 ... Sealing glass, 4 ... Lead pin, 5 ... Base, 6 ... Flow rate detection element, 11 ... Fluid, 15 ... Channel groove, 16 ... Convex part, 20 ... For channel Groove, 21 ... convex portion.

Claims (3)

In a flow sensor comprising a flow rate detection element provided with temperature detection means for detecting the temperature of the fluid, a pedestal on which the flow rate detection element is mounted, and a sealing glass for sealing the pedestal in a case,
A flow sensor characterized in that the pedestal is formed of glass, ceramics or the like having a melting point higher than that of the sealing glass, and an upper end portion of the pedestal is protruded from the sealing glass and the flow rate detecting element is fixed to the upper surface thereof. . The flow sensor according to claim 1,
A flow sensor characterized in that a flow path groove is formed along a fluid flow direction on an upper surface to which a flow rate detection element of a base is fixed. The flow sensor according to claim 1 or 2,
A flow sensor characterized in that the lower end of the pedestal is located in the sealing glass and does not protrude outside.

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