JP6043833B2 - Thermal flow meter - Google Patents

Description

  The present invention relates to a thermal air flow meter that installs a heating resistor in a fluid to be measured and measures the flow rate, and more particularly to an air flow meter suitable for measuring the intake air flow rate and exhaust gas flow rate of an internal combustion engine of an automobile. Involved.

  As an air flow meter for detecting an intake air amount of an internal combustion engine such as an automobile, a thermal air flow meter capable of directly measuring a mass flow rate is a mainstream.

  In recent years, it has been proposed to manufacture a sensor element of a thermal flow meter on a semiconductor substrate such as silicon (Si) using micromachine technology. In such a semiconductor type sensor element, a hollow portion is formed by removing a part of a semiconductor substrate in a rectangular shape, and a heating resistor is formed on an electrical insulating film of several microns formed in the hollow portion, that is, a thin film portion. ing. Also, it is possible to distinguish between forward and reverse flow by forming a temperature sensor (temperature sensitive resistor) in the vicinity of the heating resistor and detecting the flow rate from the temperature difference between the upstream and downstream of the heating resistor. is there. Since the size of the heating resistor is as small as several hundred microns and is formed in a thin film shape, the heat capacity is small and high-speed response and low power consumption are possible.

  There exists a thing of patent document 1 regarding the mounting structure of the sensor element and drive circuit in an air flowmeter which has such a semiconductor type sensor element, and what is called chip packaging.

  In Patent Document 1, a sensor chip for detecting a flow rate of fluid, a lead as an external connection terminal electrically connected to the sensor chip, and a connection part between the sensor chip and the lead are covered, and the flow rate detection unit is exposed. The thing of the structure provided with the sealing resin arrange | positioned integrally is disclosed. Further, FIG. 2 of Patent Document 1 shows an example in which a driving chip and a sensor chip are mounted on a metal lead frame and sealed with a resin.

JP 2008-175780 A

  Air flow meters with semiconductor-type sensor elements that are currently in practical use have sensor elements and drive circuits mounted on a ceramic substrate such as LTCC (Low Temperature Co-fired Ceramics), and the substrate is placed inside the product body. The one with the implemented configuration is the mainstream. As the drive circuit, an LSI integrated into one chip by a semiconductor integration technique is used from the viewpoint of mountability. Further, in order to protect the drive circuit from disturbance noise such as surge and radio wave interference, a chip capacitor is separately provided on the ceramic substrate and is electrically connected. A chip capacitor for protecting the drive circuit from this noise has a large capacity, and is often arranged externally on the ceramic substrate without being arranged in the LSI.

  On the other hand, most of the thermal air flow meters for automobiles have a configuration in which an air temperature detection element for detecting the temperature of air taken into the engine is integrated. This detection of the air temperature is taken into the engine control unit and used to control the combustion of the engine regardless of the measurement of the air flow rate. In particular, it is indispensable for engine combustion control in a transient state such as early activation of the catalyst at the time of cold start and reduction of NOx in exhaust exhausted when the engine state suddenly changes after engine warm-up. Also from this purpose of use, the temperature detecting element is required to have high-speed response.

  There are a number of means for temperature detection, but due to these requirements, thermistor elements are often used, and in particular, an element called an axial lead type in which lead wires are arranged on almost the same straight line in the axial direction is often used. Yes. Further, this axial lead type temperature detecting element is connected and fixed to a lead terminal inserted in a resin casing of the air flow meter by welding.

  As described above, the structure is complicated because the chip capacitor constituting the protection circuit for protecting the drive circuit and the element for detecting the temperature of the intake air are individually mounted.

  An object of the present invention is to provide a thermal flow meter that is highly accurate, highly reliable, and has a simple structure and is less expensive.

  In order to achieve the above object, a thermal flow meter of the present invention includes a sensor element having a heating resistor formed in a diaphragm, a temperature detection element, and a drive circuit electrically connected to the sensor element, In the thermal flow meter comprising: the sensor element, the drive circuit, a metal lead frame for mounting the sensor element and the drive circuit, and the temperature detection element are sealed with resin. A chip package formed, and the chip package has an exposed structure in which a surface of the sensor element including the diaphragm is exposed, and the temperature detection element is disposed on the lead frame via a conductive member. Has been implemented.

  According to the present invention, it is possible to provide a thermal flow meter that is highly accurate, highly reliable, and has a simple structure and is less expensive.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of the plane of the chip package which shows the 1st Embodiment of this invention. 1 is a cross-sectional view of a chip package showing a first embodiment of the present invention. Sectional drawing of the chip package which shows the 2nd Embodiment of this invention. The block diagram of the thermal type flow meter which mounted the chip package which is the 2nd Embodiment of this invention. The block diagram of the plane of the chip package which shows the 2nd Embodiment of this invention. FIG. 5 is a plan configuration diagram of a chip package showing a third embodiment of the present invention. The block diagram of the thermal type flow meter which mounted the chip package which is the 3rd Embodiment of this invention. FIG. 10 is a plan configuration diagram of a chip package similar to the third embodiment of the present invention. The block diagram of the thermal type flow meter which mounted the chip package similar to the 3rd Embodiment of this invention. Sectional drawing of the suitable chip package based on the 2nd Embodiment of this invention.

  Embodiments according to the present invention will be described below.

  1 and 2 show the configuration of a chip package according to the first embodiment of the present invention. In FIG. 1, a chip package 1 includes a sensor element 2, a drive circuit 3, a chip capacitor 4, and a chip thermistor 5 that are directly mounted on a lead frame 6 that is a metal substrate, and the sensor element 2, drive circuit 3, drive circuit 3, and lead. The frames 6 are electrically connected by gold wire 8a and 8b, respectively. The lead frame 6 on which the sensor element 2, the drive circuit 3, the chip capacitor 4, and the chip thermistor 5 which are these chip parts are mounted has a configuration in which the entire periphery is sealed with a thermosetting resin 9 by molding. .

  As shown in the sectional view of FIG. 2, the chip components including the sensor element 2 are bonded and fixed to the lead frame 6 via adhesives 7a and 7b. In particular, the conductive adhesive 7b of the chip capacitor 4 and the chip thermistor 5 shown in FIG. 1 needs to use a conductive adhesive in order to ensure electrical connection between the electrode parts of the chip components and the lead frame 6. The sensor element 2 for measuring the flow rate to be measured has a hollow portion 10 formed in a semiconductor substrate, and a thin film portion 11 having a thickness of several microns is formed. The thin film portion 11 is formed with a heat generating resistor and a temperature sensitive resistor in the vicinity thereof through an electric insulating film. The thin film portion is heated by the heat generating resistor and depends on the flow rate change of the fluid flowing on the surface. The mass flow rate is measured by detecting the change in the temperature distribution of the thin film portion which is caused by a temperature-sensitive resistor formed around the thin film portion. Based on these measurement principles, the thin film portion 11 of the sensor element 2 is partially exposed from the thermosetting resin 9 covering the periphery and sealed with resin.

  In addition, aluminum electrodes are formed on the outer periphery of the sensor element 2 and the drive circuit 3, and the sensor element 2 and the drive circuit 3 are directly connected between the aluminum electrodes by a gold wire 8a, and further driven. The power source, GND or output aluminum electrode of the drive circuit different from the aluminum electrode of the circuit 3 and the lead frame 6 are connected by a gold wire 8b. In the drive circuit 3, the temperature of the heating resistor formed in the sensor element 2 and the signal detected by the sensor element 2 are converted into a signal converted into a flow rate. These flow rate signals are taken in and taken out from the input / output terminal 12 protruding from the thermosetting resin 9 from the drive circuit 3 through the gold wire 8b.

  FIGS. 1 and 2 show a configuration in which the chip capacitor 4 that protects the drive circuit 3 and the chip thermistor 5 of the air temperature detecting element are simultaneously sealed with resin, but only one of them is mixedly mounted inside the chip package 1. It may be the configuration. In either case, the configuration of the thermal flow meter is simplified and the subsequent production process can be simplified, so that the effects of the present invention can be obtained.

  Here, the problem in the structure which resin-seals the semiconductor type sensor element like this proposal is described. As described with reference to FIG. 2, the sensor element 2 has a cavity 10 formed therein and has a thin film portion 11 on the order of several microns. The thinness of the thin film portion 11 greatly contributes to the high-speed response that is a feature of the thermal type flow meter using a semiconductor type element. On the other hand, since the thin film portion 11 is thin, it is sensitive to mechanical stress and stress applied by expansion and contraction due to heat, and attention is particularly required in the production process. Due to such characteristics, when the thermosetting resin 9 is molded, if the molding die directly touches the thin film portion 11, the thin film portion 11 may be damaged or cracked. Further, when the cavity 10 of the sensor element 2 is sealed with the thermosetting resin 9, the air sealed inside repeatedly expands and contracts depending on the surrounding temperature change and the like, and stress is applied to the thin film portion 11 to detect the flow rate. There are concerns about adverse effects on the

  In order to avoid these problems, when the chip package of the present invention is molded, for example, a relief (concave shape) is provided at a position where it contacts the thin film portion 11 of the molding die, and the thin film portion 11 is not directly touched. It is good to mold by a form and to expose partially the thin film part 11 of the sensor element 2 from the thermosetting resin 9 after shaping | molding. Further, as to the problem when sealing the cavity 10 of the sensor element 2, as shown in the cross section of the chip package according to the second embodiment of the present invention shown in FIG. It is preferable that the function as the passage 13 is provided in advance, and the outlet portion 14 of the passage 13 is partially suppressed by a molding die at the time of molding, and the outlet portion 14 is connected to the outside of the chip package 1. Thereby, since the cavity 10 of the sensor element 2 is always in communication with the outside of the thermosetting resin 9, the expansion and contraction of the air in the cavity 10 caused by the change in ambient temperature is caused by the thermosetting resin 9. Stress is not applied to the thin film portion 11 by being absorbed by escape or suction to the outside.

  Next, a preferred arrangement of chip components to be mounted inside the chip package will be described with reference to FIGS.

The main points of mounting the chip package on the thermal flow meter will be described with reference to FIG. FIG. 4 shows a configuration when the chip package whose cross section is shown in FIG. 3 is mounted on a thermal flow meter. The chip package 1 is fixed to the housing 15 of the thermal flow meter. About this fixing method, it is good to adhere | attach with the thermosetting type adhesive agent conventionally used in many things. As other means, there is no particular problem even if a room temperature curable adhesive or a mechanical fixing means is used.
A sub-passage 17 for taking in air flowing through the intake pipe 16 is formed at the tip of the housing 15. The auxiliary passage 17 constitutes a passage by a cover arranged so as to sandwich the housing 15. The thin film portion 11 of the sensor element 2 exposed from the thermosetting resin 9 of the chip package 1 and the chip thermistor 5 that detects the temperature of the air are disposed in the housing 15 so as to be disposed in the sub-passage 17. In addition, as for the shape of the sub-passage 17, FIG. 4 shows an example of a straight pipe-type passage shape, but a passage shape that swirls air taken into the sub-passage such as a bypass shape may be applied. . The drive circuit 3 and the chip capacitor 4 of other chip components sealed in the resin of the chip package 1 are disposed in the circuit chamber 18, and the boundary 19 between the sub passage 17 and the circuit chamber 18 is the sub passage 17 and the circuit chamber. It is partitioned using a means that can keep the airtightness between 18. The input / output terminal 12 protruding from the chip package 1 is connected to the connector terminal 21 in the circuit chamber 18 by welding or the like, and a signal is output from the connector 20.

FIG. 5 shows a plan view of the chip package shown in FIG. As described above, the sensor element 2 for detecting the flow rate and the drive circuit 3 are mounted on the lead frame 6 and electrically connected by the gold wire 8a. In the case of bonding connection with a gold wire, it is preferable that the sensor element 2 and the drive circuit 3 are close to about 2 to 4 mm because of restrictions on the loop height and length of the gold wire. The width and length of the lead frame 6 where the sensor element 2 and the drive circuit 3 are mounted are limited by the size of the sensor element 2 and the drive circuit 3 and the turning of the input / output terminals 12.
In view of these circumstances, it is considered optimal that the outer shape of the chip package 1 is basically rectangular with a minimum size in accordance with the size and arrangement of the mounted chip components.

  Next, with reference to FIG. 3 and FIG. 5, the configuration and arrangement of the passage formed between the cavity portion formed in the sensor element and the outside of the thermosetting resin and the outlet portion thereof will be described. The passage 13 shown in FIG. 3 is most efficiently formed in parallel with the arrangement of the chip components from the shape of the lead frame 6 where the sensor element 2 and the drive circuit 3 are mounted. That is, it is preferable to form it immediately below the sensor element 2 and the drive circuit 3. In the above, when the outlet portion 14 of the passage 13 is provided between the sensor element 2 and the drive circuit 3, it is practically impossible to form the wire 13 in order to cross with the gold wire 8a. Therefore, as shown in FIG. 5, it is preferable that the outlet portion 14 be provided at a position opposite to the arrangement of the sensor element 2 around the drive circuit 3. For these reasons, the sensor element 2, the drive circuit 3, and the cavity portion 10 of the sensor element 2 are arranged in the same linear direction with the outlet portion 14 communicating with the outside of the thermosetting resin 9, and the sensor element 2 and the outlet portion 14 are connected. If the drive circuit 3 is disposed between the chip circuits, chip components can be efficiently disposed, and the size of the chip package 1 can be reduced.

  As shown in the plan configuration of the chip package according to the embodiment of the present invention in FIGS. 1 and 5, the shape of the thermosetting resin 9 covering the entire lead frame 6 on which the chip components are mounted is the front of the chip package 1. When viewed from the perspective, the chip package 1 is a symmetrical rectangular chip package 1. In the case of this configuration, the chip thermistor 5 that detects the air temperature is sealed with the thermosetting resin 9 in the same manner as other chip components. Therefore, there is a possibility that the followability with respect to the temperature change of the air, that is, the response is deteriorated. In addition, there is a concern that the temperature detection accuracy of the fluid to be measured may decrease due to heat transfer via the intake pipe or the flow meter housing through the thermosetting resin 9 or the lead frame 6 that seals the entire circumference. Is done. This problem can be improved by the following measures.

  Next, a preferred arrangement of the chip thermistor for detecting the temperature of the fluid to be measured and the chip package structure will be described with reference to FIGS. FIG. 6 shows a plan view of a chip package showing a third embodiment of the present invention. In order to overcome the above problems, the lead frame 6 on which the chip thermistor 5 is mounted may be extended and mounted, and the shape of the sealing resin 9 may be different from the mounting portion of the chip thermistor 5 only. By doing so, it is possible to suppress an adverse effect on temperature detection due to a pseudo heat capacity increase or heat transfer from the thermosetting resin 9 or the lead frame 6.

FIG. 7 shows an example in which the chip package according to the third embodiment of the present invention is mounted on a thermal flow meter. As a preferable method for mounting the chip package 1 on the housing 15, a chip thermistor 5 is used. The arrangement is preferably arranged upstream of the flow of the intake air when mounted on the casing 15 of the thermal flow meter, that is, at a location where direct air collides. By arranging it at a location where air directly collides, it is possible to detect a change in the temperature of the air faster and with higher accuracy.
In FIG. 4, the flow rate detection unit 11 of the sensor element 2 and the chip thermistor 5 are arranged in the same sub-passage 17. The sub-passage 17 may have various shapes such as a detour shape. When the chip package described with reference to FIG. 6 is applied to such a detour-shaped sub-passage 17, the sensor element 2 is disposed in the sub-passage 17. The chip thermistor 5 is preferably arranged directly in the intake pipe line 16. By doing in this way, the detection of the air temperature in the chip thermistor 5 can be detected with high accuracy without depending on the shape of the sub passage 17.

  Next, another plan of the third embodiment will be described with reference to FIGS. FIG. 8 is a configuration diagram of the chip package plane of the alternative. The arrangement of the chip thermistor 5 is characterized in that the chip thermistor 5 is arranged at a position opposite to the protruding direction of the input / output terminal 12 protruding from the thermosetting resin 9 of the chip package 1, that is, at the front end side of the chip package 1. Also in this configuration, the lead frame 6 on which the chip thermistor 5 is mounted is extended, and the shape of the sealing resin 9 is a shape that protrudes only from the mounting portion of the chip thermistor 5. The resulting effect is obtained as well. FIG. 9 shows an example of the configuration when this alternative chip package is mounted on a thermal flow meter. When the sub-passage 17 has a straight pipe shape, the sensor element 2 is arranged in the sub-passage 17 and the tip The mounting portion of the chip thermistor 5 protruding to the side may be disposed in the intake pipe line 16.

  A preferred embodiment relating to the thickness of the chip package of the present invention will be described by comparing FIG. 3 and FIG. First, T1 shown in FIG. 3 is the thickness of the chip package of the second embodiment. Assuming that it is mounted on a thermal flow meter, the upper limit of the thickness of the chip package is determined from the width of the housing and the degree of mounting freedom in the chip package proposed in the present invention. If it is too thin, it will naturally bounce off due to insufficient strength, so there is also a lower limit value. However, from the viewpoint of freedom of layout, it is necessary to suppress the thickness of the chip package as much as possible.

  In the example of FIG. 3, one factor determining the thickness of the chip package is the loop height of the gold wire 8a, 8b. The loop height of the gold wire 8a or 8b is the height of the sensor element 2 or drive circuit 3 to be connected, the step height of the lead frame 6 (the distance from the surface of the chip component to the chip component mounting surface of the lead frame). ). In other words, from the viewpoint of reducing the thickness of the chip package 1, it can be said that it is advantageous to apply different sensor elements 2 and drive circuits 3 to the chip height.

  FIG. 10 shows an example in which the height of the drive circuit 3 is lower than the height of the sensor element 2, but in such a combination, the height of the drive circuit 3 is reduced by the amount of the gold wire 8a, 8b. Since it is assigned as the loop height, the highest point of the resulting gold wire 8a, 8b can be lowered, and the thickness of the chip package 1 can be reduced (T1> T2). Further, in the relationship between the chip height of the sensor element 2 and the drive circuit 3, a combination in which the chip height of the sensor element 2 is lower than the chip height of the drive circuit can obtain the same effect. There is no particular problem even if it is applied.

1 Chip Package 2 Sensor Element 3 Drive Circuit 4 Chip Capacitor (Protection Circuit)
5 Chip thermistor (air temperature detection element)
6 Lead frame 7a Adhesive 7b Conductive adhesive 8a, 8b Gold wire 9 Thermosetting resin (sealing resin)
10 Cavity part 11 Thin film part (flow rate detection part)
12 I / O terminal 13 Passage 14 Exit 15 Housing 16 Intake pipe 17 Sub-passage 18 Circuit chamber 19 Boundary 20 Connector 21 Connector terminal

Claims (8)

In a thermal flow meter comprising a sensor element having a heating resistor formed in a diaphragm, a temperature detection element, and a drive circuit electrically connected to the sensor element,
Resin comprising the sensor element, the drive circuit, a metal lead frame for mounting the sensor element and the drive circuit, and the temperature detection element mounted on the lead frame via a conductive member A chip package formed by sealing with,
A sub-flow channel that takes in part of the fluid to be measured flowing through the main flow channel,
The chip package has an exposed structure in which a surface of the sensor element including the diaphragm is exposed ,
The chip package includes a thermal flowmeter provided such that a portion where the sensor element is mounted is located in the sub-flow path and a portion where the temperature detection element is mounted is positioned in the main flow path .   The thermal flow meter according to claim 1, wherein the chip package has a shape in which a portion on which a temperature detection element is mounted protrudes.   The thermal flow meter according to claim 2, wherein the protruding direction is a direction on the upstream side of the flow of the fluid to be measured.   The thermal flow meter according to claim 2, wherein the protruding direction is a direction perpendicular to the flow of the fluid to be measured. The chip package is
It has a connection terminal for electrical connection with the outside of the chip package,
The thermal flow meter according to claim 2, wherein the thermal flow meter has a shape protruding in a direction perpendicular to the connection terminal. The chip package is
It has a connection terminal for electrical connection with the outside of the chip package,
The thermal flow meter according to claim 2, wherein the connection terminal has a shape protruding in a horizontal direction.   The metal lead frame includes a mounting part on which the driving circuit is mounted and a protruding part protruding from the mounting part, and the temperature detection element is mounted on the protruding part. Thermal flow meter. The thermal flow meter according to claim 1, wherein the chip package includes a capacitor mounted on the lead frame, and the capacitor is sealed with the resin.

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