WO2016002439A1

WO2016002439A1 - Thermal air flowmeter

Info

Publication number: WO2016002439A1
Application number: PCT/JP2015/066423
Authority: WO
Inventors: 公俊緒方; 石塚　典男; 忍田代; 徳安　昇
Original assignee: 日立オートモティブシステムズ株式会社
Priority date: 2014-06-30
Filing date: 2015-06-08
Publication date: 2016-01-07
Also published as: JP6336833B2; JP2016011887A

Abstract

The purpose of the present invention is to improve the measurement accuracy of a thermal air flowmeter. The thermal air flowmeter is equipped with a sensor assembly having a lead frame, a plate provided on the lead frame, a sensor chip provided on the plate, and a resin provided so as to expose a diaphragm portion of the sensor chip, wherein the diaphragm portion is provided so as to be positioned in a sub-passage. In the thermal air flowmeter, the plate has a groove or a partially thin reduced thickness portion outside a sensor chip mounting surface region where the plate receives a press load from the sensor chip during resin molding. Alternatively, in another embodiment, the side surface of the plate is substantially flush with the side surface of the sensor chip at least in the sensor chip mounting region.

Description

Thermal air flow meter

The present invention relates to a flow meter that measures the flow rate of a gas to be measured, and more particularly to a thermal air flow meter that measures the intake air amount of an internal combustion engine.

A thermal air flow meter that measures the gas flow rate has a flow rate detection unit for measuring the flow rate, and measures the gas flow rate by transferring heat between the flow rate detection unit and the gas to be measured. It is configured as follows. The flow rate measured by the thermal air flow meter is widely used as an important control parameter in various apparatuses. A feature of the thermal air flow meter is that a gas flow rate, for example, a mass flow rate can be measured with relatively high accuracy compared to other types of flow meters.

However, further improvement in gas flow measurement accuracy is desired. For example, a vehicle equipped with an internal combustion engine has a very high demand for fuel saving and exhaust gas purification. In order to meet these demands, there is a need for highly accurate measurement and high-speed response of the intake air amount, which is a main parameter of an internal combustion engine. A thermal air flow meter that measures the amount of intake air led to an internal combustion engine includes a sub-passage that takes in a part of the intake air amount and a sensor chip disposed in the sub-passage, and a flow rate detection unit provided in the sensor chip is covered. By performing heat transfer with the measurement gas, the state of the gas to be measured flowing through the sub-passage is measured, and an electric signal representing the amount of intake air guided to the internal combustion engine is output. The sensor chip has a partial cavity formed in a semiconductor substrate by a semiconductor machining technique and a thin film part provided so as to cover the cavity. The thin film part is called a diaphragm, and the response speed of the thermal air flow meter can be further increased by forming the flow rate detection part on the diaphragm. However, when a stress is applied to the resistor arranged on the diaphragm, the resistance value changes due to the piezo effect, which becomes an error factor when measuring the flow rate. Therefore, a technique for suppressing the stress generated on the diaphragm is required. Such a technique is disclosed in Patent Document 1, for example.

WO2013084259A1

In the technique described in Patent Document 1, a sensor chip having a diaphragm structure composed of a thin film portion which is a flow rate detection portion is mounted on a plate, and a cavity on the back surface of the diaphragm and outside air are passed through an air passage and an air hole formed in the plate. Connect. After sealing the sensor chip and plate with the diaphragm surface serving as a flow rate detection unit exposed, the diaphragm surface is disposed in the sub-passage for measuring the flow rate, and the air hole connecting the rear surface of the diaphragm and the outside air is formed as a sub-port. Place outside the aisle. According to this technique, it is possible to reduce the pressure difference between the front and back surfaces of the diaphragm caused by a temperature change during flow rate measurement, and to suppress warping that occurs in the diaphragm. Therefore, the stress generated in the diaphragm can be reduced, and a decrease in measurement accuracy can be suppressed. However, in the above structure, when the sensor chip pushes the plate at the time of resin sealing, the plate may be bent and deformed, and the sensor chip may be deformed. As a result, stress is generated in the diaphragm, which may reduce the measurement accuracy.

An object of the present invention is to provide a thermal air flow meter with high measurement accuracy.

To achieve the above object, in the thermal air flow meter of the present invention, the sensor chip and the plate are molded with resin so that a diaphragm of the sensor chip and a part of the plate are exposed, and the plate is In the molding, the plate has a groove or a thinned portion that is partially thinned outside the sensor chip mounting surface area that receives a pressing load from the sensor chip.

According to the present invention, it is possible to provide a thermal air flow meter with high measurement accuracy.

It is a top view of the mounting component in a sensor assembly in the 1st example concerning this application. It is a top view of the sensor assembly in the 1st example concerning this application. It is sectional drawing of the sensor assembly in 1st Example which concerns on this application. It is sectional drawing at the time of sensor assembly preparation in 1st Example which concerns on this application. It is a thermal type air flow meter top view in the 1st example concerning this application. It is sectional drawing of the thermal type air flowmeter in 1st Example which concerns on this application. It is the top view and sectional view of a plate in the 1st example concerning this application. It is sectional drawing at the time of sensor assembly preparation in 1st Example which concerns on this application. It is the top view and sectional view of a plate in the 1st example concerning this application. It is the top view and sectional view of a plate in the 1st example concerning this application. It is the top view and sectional view of a plate in the 2nd example concerning this application. It is a top view of the plate in the 2nd example concerning this application. It is the top view and sectional view of a plate in the 2nd example concerning this application. It is the top view and sectional view of a plate in the 2nd example concerning this application. It is the top view and sectional view of a plate in the 3rd example concerning this application. It is the top view and sectional view of a plate in the 3rd example concerning this application. It is the top view and sectional view of a plate in the 4th example concerning this application. It is sectional drawing and the enlarged view of the plate in 5th Example which concerns on this application. It is sectional drawing and the enlarged view of the plate in 5th Example which concerns on this application. It is the top view and sectional view of a plate in the 6th example concerning this application. It is the top view and sectional view of a plate in the 7th example concerning this application. It is the figure which showed the air passage position dependence of the stress which generate | occur | produces in the air passage part of the plate in 7th Example which concerns on this application.

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

First, a first embodiment of the thermal air flow meter will be described. FIG. 1 is a plan view of a mounted part before the sensor assembly 10 is formed, FIG. 2 is a plan view after the sensor assembly 10 is formed, FIG. 3A is a cross-sectional view along AA in FIG. 2, and FIG. FIG. 3 is a sectional view taken along line BB in FIG. As shown in FIG. 1, the sensor assembly 10 includes a lead frame 1, a plate 2, an LSI 3, and a sensor chip 4, and these are covered with a first resin 24 as shown in FIG. 2. Specifically, as shown in FIG. 3, first, the plate 2 is bonded to the lead frame 1 with the adhesive tape 5, and the LSI 3 and the sensor chip 4 are further bonded to the plate 2 with the adhesive tape 6 and the adhesive tape 7. Glue. The plate 2 has a shape having a longitudinal direction and a lateral direction, such as a rectangle, and the sensor chip 4 and the LSI 3 are arranged on the plate 2 so as to be aligned in the longitudinal direction. The plate 2 may be made of glass or resin. Next, between the LSI 3 and the sensor chip 4 and between the LSI 3 and the lead frame 1 are electrically connected using

gold wires

8 and 9 by wire bonding. These are sealed with the first resin 24 to complete the sensor assembly 10. At the time of detecting the flow rate, the air 26 flows into the diaphragm portion 27 having the flow rate detecting portion of the sensor chip 4 from the direction of the arrow in FIG. Therefore, the sensor assembly 10 has a partially exposed structure in which the first resin 24 is not present in the diaphragm portion 27 of the sensor chip 4.

FIG. 4 is a cross-sectional view when the mounted component is clamped by the upper mold 16 and the lower mold 15 in the manufacturing process of the sensor assembly 10 having the partially exposed structure. After the mold clamping, the sensor assembly 10 is manufactured by pouring the first resin 24 into the mold. By pressing the diaphragm portion 27 of the sensor chip 4 with the upper mold 16, inflow of the resin at the time of resin sealing is prevented. As a result, the sensor assembly 10 has a partially exposed structure in which the diaphragm 27 is exposed.

FIG. 5 is a front view when the sensor assembly 10 is mounted on the housing 11 including the sub-passage 12, and FIG. 6 is a cross-sectional view taken along the line AA in FIG. The housing 11 includes a sub-passage 12 for guiding the air flowing through the main passage to the sensor chip 4, holding

portions

20 and 21 of the sensor assembly 10 (to become side walls of the sub-passage), and a holding portion 14 of the lead frame 1. The sensor assembly 10 is fixed simultaneously with the formation of the housing 11 made of the second resin. At this time, the sensor chip 4 having the flow rate detection unit needs to measure the air flow rate, and thus is disposed in the sub-passage 12. FIG. 7 is a front view of the plate 2, and a CC sectional view and a DD sectional view on FIG. As shown in FIG. 7, the plate 2 has a thinned portion 30 outside the mounting area 29 of the sensor chip 4 and on the back surface side (lead frame side). The thinned portion 30 in the first embodiment is provided up to the end of the plate 2 in the short direction.

Next, the function and effect of the first embodiment will be described. In the manufacturing process of the sensor assembly 10 shown in FIG. 4, the sensor chip 4 is pushed by the upper mold 16 in order to form a partially exposed structure of the diaphragm portion 27. As a result, the surface of the plate 2 receives a pressing load from the sensor chip 4, and the back surface of the plate 2 receives a reaction force accompanying the pressing load from the lead frame 1. When the thinned portion 30 is not formed on the plate 2, the contact area between the plate 2 and the lead frame 1 is larger than the contact area between the plate 2 and the sensor chip 4 as shown in FIG. Since the force is distributed, bending deformation occurs in the plate 2. When bending deformation occurs in the plate 2, the deformation of the sensor chip 4 is promoted, and stress is generated in the diaphragm portion 27, which may reduce the measurement accuracy. In this embodiment, by providing the thinned portion 30 outside the mounting area 29 of the sensor chip 4 on the plate 2, the difference between the contact area between the plate 2 and the sensor chip 4 and the contact area between the plate 2 and the lead frame is reduced. It can be reduced in the vicinity of the sensor chip mounting area 29, and the bending deformation of the plate can be suppressed.

FIG. 7 shows a particularly preferable configuration of the thinned portion 20. The thinned portion 30 is provided on the back side (lead frame side) of the plate 2 so that the side surface on the sensor mounting region side of the thinned portion 30 and the side surface of the sensor chip 4 are substantially flush with each other. By forming the thinned portion 30 in this way, as shown in the cross-sectional view of FIG. 4B, the contact areas on the front and back surfaces of the plate 2 are substantially equal, and the reaction force received from the lead frame 1 is the sensor chip mounting area. Concentrate in the vicinity of 29. Therefore, the bending deformation of the plate 2 as shown in FIG. 8 can be further suppressed, and the flow rate measurement accuracy can be maintained with higher accuracy.

Further, as shown in FIG. 9, the air passage 13 formed in the plate 2 may be configured as one, or the outlet opening 17 may be formed directly below the mounting area 29 of the sensor chip 4 as shown in FIG. Needless to say, the same effects can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIGS. The description of the same configuration as in the first embodiment is omitted.

11 to 12, the thinned portion 30 formed on the plate 2 is arranged outside the mounting region 29 of the sensor chip 4 in the short direction of the plate and as shown in FIGS. It is the point arrange | positioned inside from the side. In other words, the thinned portion 30 is not provided up to the end of the plate 2 in the short direction. The plate 2 is produced, for example, by fragmenting wafer-like glass or resin. However, if the side surface of the plate 2 that is a cut surface is thin, the plate 2 is likely to be chipped when fragmented, and the yield may be reduced. In the present embodiment, since the thinned portion 30 is provided on the inner side of the side surface of the plate 2, it is possible to suppress the thinning of the side surface of the plate 2 and to prevent the yield from being reduced in size. Needless to say, this configuration also achieves the same effects as the previous embodiments.

As a further modification, as shown in FIG. 13 to FIG. 14, the thinned portion 30 provided on the plate 2 is connected to the air passage 13. By preventing the thinned portion 30 from being sealed, it is possible to suppress deformation of the sensor chip due to air volume fluctuation due to heat change.

Next, a third embodiment of the present invention will be described with reference to FIGS. The description of the same configuration as in the first and second embodiments is omitted.

The configuration different from the first and second embodiments is that the plate 2 is formed so that the side surface of the mounting area 29 of the sensor chip 4 and the side surface of the plate 2 are flush with each other as shown in FIG. is there.

In the modification of the third embodiment shown in FIG. 16, the plate 2 is formed so that the side surface of the mounting area 29 of the sensor chip 4 and the side surface of the plate 2 are flush with each other only in the vicinity of the side surface of the mounting area 29. . In other words, the plate 2 has a configuration in which the width in the short direction of the sensor mounting region 29 is equal to the width in the short direction (also referred to as a flow rate detection direction) of the sensor chip. Needless to say, this configuration also achieves the same effects as the previous embodiments.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The description of the same configuration as in the first to third embodiments is omitted.

The bending deformation of the plate 2 as shown in FIG. 8 decreases in proportion to the cube of the plate thickness. Therefore, when the depth d of the air passage 13 is increased, the thickness of the plate 2 immediately above the air passage is reduced and bending deformation is increased. Therefore, as shown in FIG. 17, bending deformation can be suppressed by increasing the thickness T of the plate 2 and decreasing the depth d of the air passage 13. In order to suppress the bending deformation, it is desirable that d <T / 2. On the other hand, if the depth d of the air passage 13 is smaller than the thickness t of the adhesive sheet 5 that bonds the plate 2 and the lead frame 1, the air passage 13 may be blocked by the adhesive sheet 5 when the sensor assembly 10 is manufactured. The depth d of the air passage 13 is preferably larger than the thickness t of the adhesive sheet 5 (t <d). From the above, it is preferable that the thickness T of the plate 2, the depth d of the air passage, and the thickness t of the adhesive sheet satisfy t <d <T / 2.

Next, a fifth embodiment of the present invention will be described with reference to FIGS. The description of the same configuration as in the first to fourth embodiments is omitted.

FIG. 18 is a sectional view of the plate 2 and an enlarged view of the air passage 13. For example, when glass is used for the plate 2, the air passage 13 and the thinned portion 30 of the plate 2 are formed by sandblasting. At this time, minute cracks and scratches as shown in the enlarged view of FIG. It occurs on the surface of the passage 13 and the thinned portion 30. On the other hand, when the bending change of the plate 2 as shown in FIG. 8 occurs, the air passage 13 and the thinned portion 30 become stress concentration portions, and it is preferable to reduce this stress concentration. In this embodiment, as shown in the enlarged view of FIG. 19, the surface treatment such as hydrofluoric acid treatment can remove minute cracks and scratches generated when the air passage 13 and the thinned portion 30 are formed, thereby reducing the stress concentration. it can.

Next, a sixth embodiment of the present invention will be described with reference to FIG.

In the first to fifth embodiments, the configuration in which the air passage 13 is provided in the plate 2 and the back surface of the diaphragm portion 27 is not sealed has been described. However, the present invention is also effective in a structure in which the back surface of the diaphragm portion 27 is sealed without providing the air passage 13. When the back surface side of the diaphragm portion 27 is sealed, a pressure difference is generated on the front and back surfaces of the diaphragm portion 27 due to expansion and contraction of air due to a temperature change during flow rate measurement, and the diaphragm portion 27 is warped and deformed due to this pressure difference. It can be a flow measurement error. Further, as a factor of the flow measurement error, there is a warp of the diaphragm portion due to the deformation of the plate. According to the inventions described in the first to fifth embodiments of the present invention, the deformation of the plate can be suppressed. It becomes possible. Therefore, even when the diaphragm portion 27 is sealed, the temperature change at the time of flow rate measurement is measured, and the measurement error due to the warp deformation generated in the diaphragm portion 27 is corrected, thereby suppressing a decrease in measurement accuracy. Is possible.

Next, a seventh embodiment of the present invention will be described with reference to FIGS.

The structure different from the previous embodiment is that the air passage 13 provided in the plate 2 is provided inside the region 31 where the sensor chip 4 presses the plate 2, and the air passage 13 is formed only in the longitudinal direction of the plate 2, and the outlet This is a point communicating with the opening 17.

The function and effect of this embodiment will be described. When the sensor assembly 10 is formed, the plate 2 receives a compressive load from the pressing region 31 of the sensor chip 4 due to the clamp of the lower mold 15 and the upper mold 16, and stress concentrates in the air passage 13. FIG. 22 shows the ratio W1 / W2 between the distance W1 from the center of the air passage 13 and the distance W2 from the center of the pressing region 31 of the sensor chip 4 and the stress (W1 generated in the air passage 13 for the DD cross section of FIG. /W2=1.1 ratio of generated stress). As shown in FIG. 22, when the air passage 13 is provided immediately below the sensor chip pressing region 31 (W1 / W2 = 1.0), the air passage 13 tends to concentrate stress. In this embodiment, the air passage 13 provided in the plate 2 is provided inside the region 31 where the sensor chip 4 presses the plate 2. Thereby, the air passage 13 can be provided so as to avoid the high stress region directly below the sensor chip pressing region 31, and the stress generated in the air passage 13 can be reduced. Furthermore, by forming the air passage 13 only in the longitudinal direction of the plate 2 and communicating with the outlet opening 17, it is possible to reduce the thickness reduction region of the plate 2 due to the formation of the air passage 13. Since the bending rigidity of the plate 2 is improved as the thickness reduction region is smaller, the bending deformation of the plate 2 when the sensor assembly 10 is formed can be suppressed, and a more reliable sensor assembly 10 can be provided.

Needless to say, the effects of this embodiment can be obtained by combining or combining with the previous embodiment.

1 ... Lead frame 2 ... Plate 3 ... LSI
DESCRIPTION OF SYMBOLS 4 ... Sensor chip 5 ... Adhesive tape 6 ... Adhesive tape 7 ... Adhesive tape 8 ... Gold wire 9 ... Gold wire 10 ... Sensor assembly 11 ... Housing 12 ... Sub-passage 13 ... Air passage 14 ... Holding part
15 ... Lower mold 16 ... Upper mold 17 ... Outlet opening 20 ... Holding part 21 ... Holding part
24 ... 1st resin 26 ... Air 27 ... Diaphragm part 28 ... Hollow part 29 ... Sensor chip mounting area 30 ... Thinning part 31 ... Sensor chip pressing area

Claims

A sensor assembly having a lead frame, a plate provided on the lead frame, a sensor chip provided on the plate, and a resin provided to expose a diaphragm portion of the sensor chip;
In the thermal air flow meter provided so that the diaphragm portion is located in the sub passage,
The thermal air flowmeter according to claim 1, wherein the plate has a thinned portion on the outer side in the short direction of the plate with respect to the sensor chip mounting region.
The thermal air flow meter according to claim 1, wherein the thinned portion is a groove provided in a plate.
2. The thermal air flow meter according to claim 1, wherein the thinned portion is provided up to an end in a short direction of the plate.
The thermal air flow meter according to any one of claims 1 to 3, wherein the plate has an air passage for communicating the rear surface of the diaphragm portion with the outside of the sensor assembly.
The thermal air flowmeter according to claim 4, wherein the thinned portion and the air passage are communicated with each other.
The relationship between the thickness t of the adhesive sheet for bonding the plate and the lead frame, the thickness T of the plate, and the air passage depth d is such that t <d <T / 2. The thermal air flowmeter according to claim 4, wherein
The thermal air flow meter according to claim 4, wherein the air passage and the thinned portion are subjected to a surface treatment by a hydrofluoric acid treatment.
A sensor assembly having a lead frame, a plate provided on the lead frame, a sensor chip provided on the plate, and a resin provided to expose a diaphragm portion of the sensor chip;
In the thermal air flow meter provided so that the diaphragm portion is located in the sub passage,
The thermal air flow meter according to claim 1, wherein a side surface of the plate is substantially flush with a side surface of the sensor chip at least in the sensor chip mounting region.
The thermal air flow meter according to claim 1 or 8,
The plate has an air passage for communicating the rear surface of the diaphragm portion with the outside of the sensor assembly;
The air passage is formed on the inner side of the portion pressed against the sensor chip in the short direction of the plate,
And the said air passage is only a shape extended in a longitudinal direction, The thermal type air flowmeter characterized by the above-mentioned.