Thermal-type flowmeter
Provided is a thermal-type flowmeter which can prevent a reduction of flow rate accuracy and reliability, and an increase of cost of the thermal-type flowmeter compared to the related art, and can add a function of an electrostatic scattering mechanism. The thermal-type flowmeter of the present invention includes a sub-passage into which part of a measurement target gas flowing in a main passage is taken, a flow rate detection element of a flow measurement unit which is disposed in the sub-passage, a circuit package which supports the flow rate detection element, and a substrate to which the circuit package is fixed. The flow rate detection element includes a detection surface to detect a flow rate of the measurement target gas. The detection surface is disposed to face the circuit substrate.
1. A thermal-type flowmeter which is attached to a main passage, the thermal-type flowmeter comprising:
a sub-passage into which part of a measurement target gas flowing in the main passage is taken;
a flow rate detection element which is disposed in the sub-passage;
a supporting body which supports the flow rate detection element; and
a circuit substrate to which the supporting body is fixed,
wherein the flow rate detection element includes only in one surface thereof a detection surface to detect a flow rate of the measurement target gas, and is disposed such that the detection surface faces the circuit substrate.
2. The thermal-type flowmeter according to claim 1 ,
wherein, in the circuit substrate, a GND wire is disposed at a position to face the detection surface of the flow rate detection element.
3. The thermal-type flowmeter according to claim 1 ,
wherein the supporting body includes a guide portion in which a passage portion formed in cooperation with the circuit substrate in the sub-passage is set to be a flow passage with a cross-sectional area smaller than another passage portion connected to both ends of the passage portion.
4. The thermal-type flowmeter according to claim 3 ,
wherein the supporting body includes a resin package in which part of the flow rate detection element, a lead frame where the flow rate detection element is mounted, some of input/output terminals, and a circuit component are integrally sealed by a resin material,
wherein the detection surface of the flow rate detection element is exposed from a surface of the resin package,
wherein the guide portion is formed of the resin material, and
wherein the input/output terminal forms a fixing portion which fixes the supporting body to the circuit substrate.
5. The thermal-type flowmeter according to claim 3 ,
wherein the supporting body includes a resin package in which a circuit component, a lead frame where the circuit component is mounted, and some of input/output terminals are integrally sealed by the resin material,
wherein the guide portion is formed of the resin material, and
wherein the input/output terminal forms a fixing portion which fixes the supporting body to the circuit substrate.
6. The thermal-type flowmeter according to claim 3 ,
wherein the flow rate detection element is integrally formed with a circuit component,
wherein the supporting body includes a resin package in which part of the flow rate detection element, a lead frame where the flow rate detection element is mounted, and some of input/output terminals are integrally sealed by the resin material,
wherein the detection surface of the flow rate detection element is exposed from a surface of the resin package,
wherein the guide portion is formed of the resin material, and
wherein the input/output terminal forms a fixing portion which fixes the supporting body to the circuit substrate.
7. The thermal-type flowmeter according to claim 1 , further comprising:
a conductive lead frame in which the flow rate detection element is mounted,
wherein the lead frame forms a fixing portion which fixes the supporting body to the circuit substrate.
8. The thermal-type flowmeter according to claim 1 ,
wherein the supporting body includes a positioning portion which determines a position with respect to the circuit substrate.
9. The thermal-type flowmeter according to claim 8 ,
wherein the positioning portion is configured by at least one of a dummy pin, an adjustment pin, and a terminal which is not used for transferring a signal at a normal usage.
10. The thermal-type flowmeter according to claim 4 ,
wherein the resin package includes a plurality of connection terminals, and
wherein the plurality of connection terminals are connected and fixed to the circuit substrate by solder.
11. The thermal-type flowmeter according to claim 2 ,
wherein the GND wire is plated for protection.
12. The thermal-type flowmeter according to claim 4 ,
wherein the guide portion includes a slope which is inclined in a direction approaching the circuit substrate such that a cross-sectional area of the flow passage is gradually narrowed as the flow passage goes moves from an end of the resin package toward the detection surface of the flow rate detection element.
13. The thermal-type flowmeter according to claim 4 ,
wherein the guide portion is three-dimensionally narrowed such that a cross-sectional area of the flow passage is gradually narrowed as the flow passage goes moves from an end of the resin package toward the detection surface of the flow rate detection element.
14. The thermal-type flowmeter according to claim 3 ,
wherein the guide portion is formed in a symmetric or asymmetric shape with the detection surface interposed therebetween.
15. The thermal-type flowmeter according to claim 1 ,
wherein, in the circuit substrate, at least one physical sensor other than the flow rate detection element and a circuit component are disposed.