The present disclosure relates to packaged flow sensors.
Flow sensors that detect the flow rate, the flow velocity, and the direction of the flow of a fluid are being used. A flow sensor includes, for example, a sensor unit which includes a heater and thermopiles with the heater interposed therebetween on a thin film (membrane). In the flow sensor including such a sensor unit, when a distribution of heat generated by heating the thin film by the heater is disturbed by the flow of the fluid, this disturbance is measured as a difference in the thermal electromotive forces generated in the thermopiles. Since the sensor unit uses the membrane, it can be said that the sensor unit is a component which is easily damaged by physical contact or the like.
For example, Patent Document 1 discloses a flow sensor that is formed integrally with a channel for passing a fluid. Patent Document 2 discloses a flow sensor that is formed separately from a channel and in which a sensor unit for detecting the flow velocity is exposed outside. The flow sensor disclosed in Patent Document 2 is arranged in the channel and detects the flow rate together with the sectional area of the channel.
Since the flow sensor disclosed in Patent Document 1 is formed integrally with the channel, it is difficult to reduce the size of the flow sensor, and the manufacturing cost is high. Since the flow sensor disclosed in Patent Document 2 is formed separately from the channel, the size of the flow sensor can be reduced easily. However, the flow sensor disclosed in Patent Document 2 is difficult to handle since the exposed sensor is easily damaged by physical contact or the like.
Therefore, a packaged flow sensor in which a sensor unit is protected by housing a flow sensor in a package can be considered. In the case of the packaged flow sensor, sensor, the flow sensor detects the flow of a fluid which is introduced through a vent hole provided in the package. However, depending on the position where the vent hole is provided, the flow of the fluid may not stabilize, and the performance of the flow sensor may deteriorate.
An object of one aspect of the disclosed technique is to provide a packaged flow sensor that can stabilize the flow of a fluid.
One aspect of the disclosed technique is exemplified by a packaged flow sensor as follows. The packaged flow sensor is a packaged flow sensor for use by being fixed to an external substrate, including a flow sensor chip which includes a sensor unit configured to detect a flow rate of a fluid; a case member with an opening toward the external substrate and configured to house the sensor unit such that the sensor unit faces the opening; and a fixing member protruding from the case member toward the external substrate and fixing the packaged flow sensor to the external substrate.
Since delicate components for detecting the flow rate of a fluid are mounted on the surface of the sensor unit of the flow sensor, the sensor unit is susceptible to damage by physical contact or the like. In the disclosed technique, since the sensor unit of the flow sensor chip can be protected from physical contact or the like by housing the flow sensor chip in a package, the flow sensor can be handled easily. In addition, this packaged flow sensor is not formed integrally with a channel. Hence, this packaged flow sensor can be miniaturized more easily than a flow sensor which is formed integrally with a channel. Since the package itself is compact, the degree of freedom in attachment to a channel can be improved even when the packaged flow sensor is to be embedded to a separately formed channel to detect a flow rate from a detected flow velocity. Furthermore, the packaged flow sensor can remain compact even when it has a structure that includes a channel.
In this packaged flow sensor, the sensor unit is arranged to face the opening of the case member and is fixed to the external substrate by a fixing member in a state in which the opening faces the external substrate. Since the fixing member protrudes from the case member in the direction of the external substrate, a gap is formed between the case member and the external substrate. Fixing the packaged flow sensor to the external substrate in this manner allows the sensor unit to face the external sensor. Hence, the sensor unit can detect the flow of a fluid flowing in the gap formed between the case member and the external substrate. The gap formed between the case member and the external substrate can be used as a channel by the packaged flow sensor. Hence, the surface of the external substrate can be expected to have a flow adjustment effect that can stabilize the flow of the fluid. As a result, reduction in the sensitivity of the flow sensor chip may be restrained in the packaged flow sensor.
Furthermore, in the packaged flow sensor, since the sensor unit of the flow sensor chip faces the direction of the external substrate, the packaged flow sensor can be picked up easily when the packaged flow sensor is to be mounted on the external substrate by the tape and reel method. Hence, the productivity of the mounting process for mounting the packaged flow sensor onto the external substrate can be improved.
Note that an amount of protrusion by which the fixing member protrudes from the case member to the external substrate may be determined in accordance with the fluid velocity to be detected by the sensor unit. The channel that introduces the fluid into the sensor unit is formed by, for example, a gap which is formed between the external substrate and the case member by the fixing member. The height of the channel changes in accordance with the amount of protrusion of the fixing member. Forming a low channel restricts the introduction of the fluid into the sensor unit. That is, by decreasing the amount of protrusion, the packaged flow sensor can allow the sensor unit to detect the flow of a high velocity fluid while restricting the load placed on the sensor unit from the high velocity fluid. In addition, forming a high channel promotes the introduction of the fluid into the sensor unit. That is, by increasing the amount of protrusion, the packaged flow sensor can detect a low velocity fluid with high sensitivity.
In the packaged flow sensor, the fixing member may include a lead frame that is electrically coupled to an interconnect on the external substrate. Using the lead frame as a fixing member allows the packaged flow sensor to be fixed and electrically coupled to the external substrate at once.
In the packaged flow sensor, the case member includes a bottom plate formed in a rectangular shape and side walls which are erected from respective edges of the bottom plate toward the external substrate, and the fixing member may protrude from opposing ones of the side walls of the case member toward the external substrate. Providing the fixing member in this manner allows the fixing member to prevent the fluid from entering the gap, which is formed between the case member and the external substrate, from a direction different from the direction in which the gap extends. Hence, the flow of the fluid flowing through the channel can be further stabilized.
In the packaged flow sensor, the flow sensor chip may be arranged on the bottom plate in a state in which the sensor unit faces the opening. Arranging the flow sensor chip in this manner can reduce the height of the packaged flow sensor. That is, the miniaturization of the packaged flow sensor is facilitated.
The packaged flow sensor further includes a plate-shaped lid member that covers the opening. A first introduction hole and a second introduction hole that guide the fluid into the case member may be formed by the lid member and the opening, and the sensor unit may be arranged between the first introduction hole and the second introduction hole when viewed in a direction normal to the lid member. By providing the lid member, dust contained in the fluid can be prevented from adhering to the sensor portion. In addition, even when the opening is covered by the lid member, the fluid can be guided toward the sensor unit by providing the first introduction hole and the second introduction hole.
In the packaged flow sensor, the case member may further house a charge pump, which boosts a voltage supplied from the outside and supplies the boosted voltage to the sensor chip, or an amplifier which amplifies the output of the sensor chip. Having such a feature can suppress noise that can mix into the wiring between the sensor chip and the charge pump or the amplifier. Consequently, the performance of the packaged flow sensor can be improved.
The packaged flow sensor can stabilize the flow of a fluid.
A sensor package according to an embodiment will be described with reference to the accompanying drawings.
Hereinafter, in this specification, the side of the resin base 1 is referred to as an upper side, and the side of the lead frames 3 is referred to as a lower side. The long direction, the short direction, and the height direction of the sensor package 100 are referred to as an X direction, a Y direction, and a Z direction, respectively. The sensor package 100 is an example of a “packaged flow sensor”.
The resin base 1 is a case member that opens downward to form a housing chamber 101 for housing the flow sensor chip 2. The resin base 1 illustrated in
Each lead frame 3 is a connection terminal to an external substrate. As illustrated in
A lid 4 is a plate-shaped member that covers the opening of the resin base 1. The length in the short direction of the lid 4 is equal to the length in the short direction of the opening of the resin base 1. Further, the length in the long direction of the lid 4 is shorter than the length in the long direction of the opening of the resin base 1. The lid 4 is arranged such that its center approximately coincides with the center of the opening of the resin base 1 in a plan view. As a result, gaps are formed between the lid 4 and the opening at both ends in the long direction of the opening of the resin base 1. The gaps form vent holes 14 and 14 that allow a fluid to flow between the outside and the housing chamber 101. The vent holes 14 and 14 are examples of a “first introduction hole” and a “second introduction hole”, respectively. The lid 4 is an example of a “lid member”.
The flow sensor chip 2 is a sensor that measures the flow velocity of a fluid (for example, gas). The flow sensor chip 2 includes a body 21, which is shaped like a conical bowl and opens downward, and the sensor unit 22 which covers the opening of the body 21.
(Flow Sensor Chip 2)
The heater 23 is a heating device for heating the membrane 25. As it is a thin film, the membrane 25 has a low heat capacity and can be effectively heated by the heater 23. The thermopiles 24 and 24 are thermocouples that generate thermal electromotive force by receiving heat from the membrane 25. Since the contact point at one end of each of the thermopiles 24 and 24 is on the main body 21, the temperature difference between the membrane 25 and the main body 21 can be detected as thermal electromotive force. The thermopiles 24 and 24 generate higher thermal electromotive force as the temperature increases. When both of the thermopiles 24 and 24 have the same temperature, the thermopiles 24 and 24 generate identical thermal electromotive forces. The flow sensor chip 2 is, for example, a thermal flow sensor that heats the membrane 25 by the heater 23 and measures the flow rate based on a difference between the respective thermal electromotive forces of the thermopiles 24 and 24, which is generated by a difference in the distribution of heat in the membrane 25. The flow sensor chip 2 is manufactured by, for example, Micro Electro Mechanical Systems (MEMS).
Power supply terminals 231 and 231 for receiving power supplied to the heater 23 from an external power supply 40 are connected to the respective ends of the heater 23 in the membrane 25 of the flow sensor chip 2. Measuring terminals 243 and 243 for measuring a difference Vout between the respective thermal electromotive forces generated by the thermopiles 24 and 24 are provided in the membrane 25. Each of the thermopiles 24 and 24 is connected in series to the corresponding one of the measuring terminals 243 by an interconnect 26. The flow sensor chip 2 is, for example, a surface-mount flow sensor in which the membrane 25 including the heater 23 and the thermopiles 24 and 24 is exposed to the outside. The sensor unit 22 that includes the membrane 25, the heater 23, and the thermopiles 24 and 24 is an example of a “sensor unit”. The flow sensor chip 2 is an example of a “flow sensor chip”. Although thermopiles are used as temperature detecting elements for detecting the heat of the heater 23 here, the temperature detecting elements may be sensor chips such as diodes, thermistors, or platinum resistance thermometers or the like.
As described above, the thermal electromotive forces generated by the thermopiles 24 and 24 increase as the temperature increases. The temperature of the thermopile 24 which is located on the downstream side of the airflow becomes higher than the temperature of the thermopiles 24 located on the upstream side of the airflow. Hence, by measuring the difference (that is, V2-V1) between the thermal electromotive force V1 of the thermopile 241 and the thermal electromotive force V2 of the thermopile 242, the flow sensor chip 2 can detect the direction of the airflow and the strength of the airflow.
Since the thermopile 242 has a higher temperature than the thermopile 241 when V2-V1 is positive, the flow sensor chip 2 can detect that the air is flowing from the thermopile 241 in the direction toward the thermopile 242. Also, since the thermopile 241 has a higher temperature than the thermopile 242 when V2-V1 is negative, the flow sensor chip 2 can detect that the air is flowing from the thermopile 242 in the direction toward the thermopile 241.
Furthermore, since both of the thermopiles 24 and 24 have the same temperature when V2-V1 is 0 (zero), the flow sensor chip 2 can detect that there is no airflow (or the airflow is below the lower limit of a detection range) in such a state. The flow sensor chip 2 can detect that the air is flowing stronger as the value of V2-V1 increases. The flow sensor chip 2 is an example of a “sensor chip”.
As can be understood with reference to
The lead frames 3 protrude below the lower ends 15 of the resin base 1. That is, the lead frames 3 protrude from the lower ends 15 of the resin base 1 toward the external substrate 200. Hence, a gap D is formed between the lower ends 15 of the resin base 1 and the external substrate 200. As can be understood with reference to
A comparative example will be described. In the comparative example, the flow sensor chip 2 is provided on the lead frames 3 instead of the resin base 1.
(Method of Manufacturing Sensor Package 100)
In S1, the lead frames 3 are prepared.
In S3 of
In S4 of
In S5 of
As a reference, in the sensor package 500 according to the comparative example described above, the resin base 1a is formed after the flow sensor chip 2 is adhered to the lead frame 3 which is prepared in S1 of
In the sensor package 100 according to the embodiment, the flow sensor chip 2 is provided in the resin base 1 in a state in which the sensor unit 22 faces the external substrate 200. Since the lead frames 3 protrude from the lower ends 15 of the resin base 1 toward the external substrate 200, the gap D can be formed between the external substrate 200 and the lower ends 15 of the resin base 1. As described above, since a part of the air that flows through the gap D can be introduced to the housing chamber 101 via the vent holes 14, the sensor package 100 can detect the airflow. In addition, in the embodiment, by using the gap D as a channel, it is possible to expect the surface of the external substrate 200 to have a flow adjustment effect that can stabilize the flow of the fluid. Although the height of the gap D can change the rate of air that flows through the gap D and the housing chamber 101, the height of the gap D can be changed based on the shape (the bend height and the amount of protrusion from the resin base 1 toward the external substrate 200). Hence, the flow velocity sensitivity of the sensor package 100 can be changed based on the shape of the lead frames 3, thus allowing a desired sensitivity to be obtained.
For example, decreasing the amount by which the lead frames 3 protrude from the resin base 1 toward the external substrate 200 can lower the height of the gap D. Lowering the height of the gap D restricts the introduction of fluid into the flow sensor chip 2. That is, decreasing the amount of the protrusion of the lead frames 3 allows the sensor package 100 to detect the flow of a fluid while restricting the load from a fluid of a high velocity on the flow sensor chip 2. In addition, for example, increasing the amount by which the lead frames 3 protrude from the resin base 1 toward the external substrate 200 can raise the height of the gap D. Raising the height of the gap D promotes the introduction of fluid into the flow sensor chip 2. That is, increasing the amount of the protrusion of the lead frames 3 allows the sensor package 100 to detect the flow of the fluid with a high sensitivity even when the flow velocity of the fluid is low. Note that although the lead frames 3 are bent and protrude toward the external substrate 200 in the embodiment, the lead frames 3 may extend straight from the lower ends of the resin base 1 toward the external substrate 200.
The lid 4 covers the opening of the resin base 1 in the sensor package 100 according to the embodiment. Hence, in this embodiment, the sensor package 100 is protected by the resin base 1 and the lid 4 from physical impact and surrounding dust.
In the sensor package 100 according to the embodiment, the direction in which the gap D extends coincides with the direction in which the plurality of lead frames 3 are arrayed. Hence, the plurality of lead frames 3 can attenuate the air flowing toward the gap D from a different direction (for example, the Y direction) from the direction in which the gap D extends. Therefore, the sensor package 100 can suppress turbulence in the air flowing through the gap D, thus preventing a reduction in the fluid detection accuracy of the flow sensor chip 2.
<Modification 1>
In the embodiment, each portion bent in the Y direction at the lower end of each lead frame 3 is fixed to the corresponding interconnect on the external substrate 200 by the solder 201. Modification 1 will describe an arrangement in which the lower end of each lead frame 3 is inserted into a corresponding through hole provided in the external substrate 200.
<Modification 2>
In the housing chamber 101 formed by the resin base 1 of the sensor package, another electronic component may be further mounted in addition to the flow sensor chip 2.
<Modification 3>
In the embodiment, airflow is introduced into the housing chamber 101 through the vent holes 14 and 14 provided in the lower opening of the resin base 1. Modification 3 will describe an arrangement in which through holes are also provided in the side walls 11 and 11 of the resin base 1.
(Other Modifications)
For example, the lid 4 may be omitted in the sensor package 100. Even when the lid 4 is omitted, turbulence in the airflow introduced into the flow sensor chip 2 may be suppressed by using the gap D, which is formed between the lower ends 15 of the resin base 1 and the external substrate 200, as a channel.
In the sensor package 100, the sensor package 100 is fixed to the external substrate 200 by the lead frames 3, which are electrically coupled to the external substrate 200. However, the sensor package 100 may be fixed to the external substrate 200 by a fixing member that is not electrically coupled.
The embodiment and the modifications disclosed above can be combined.
Number | Date | Country | Kind |
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2020-040414 | Oct 2020 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/046686 | 12/15/2020 | WO |