Thermal flowmeter

Abstract

The present application provides a thermal flowmeter with high reliability. The thermal flowmeter (20) has a flow detecting element (321) that detects air flow, and a conductive coating film (400) that contains a conductive substance and a resin as constituent elements, provided on at least a portion of a position in the sub passage 135) on a surface opposite to a detecting surface (322) of the flow detecting element (321).

Description

Technical Field

[0001] This invention relates to a thermal flow meter. Background Technology

[0002] As a technology related to thermal flow meters for measuring the flow rate of the gas being measured, there is, for example, the technology described in Patent Document 1.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-7902 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the thermal flow meter described in Patent Document 1, part or all of the plate-shaped member facing the flow detection unit is formed of a conductive material, which removes charge from the pollutants contained in the measured gas. However, in the thermal flow meter described in Patent Document 1, the main passage must be made into a complex shape, and there is room for improvement in reducing the cost of achieving the charge removal function.

[0008] The present invention was made in view of the above circumstances, and its object is to provide a highly reliable thermal flow meter.

[0009] Technical means to solve the problem

[0010] To solve the above-mentioned problems, the thermal flow meter of the present invention is characterized by comprising: a flow detection element that detects air flow; and a circuit board that is partially disposed opposite to the detection surface of the flow detection element, wherein a conductive resin member comprising a conductive material and a resin is disposed on at least a portion of the surface of the circuit board opposite to the detection surface of the flow detection element and disposed in a sub-passage.

[0011] The effects of the invention

[0012] According to the present invention, a highly reliable thermal flow meter can be provided.

[0013] Other issues, structures, and effects not mentioned above will be clarified through the following description of the implementation methods. Attached Figure Description

[0014] Figure 1 This diagram illustrates the configuration of an internal combustion engine control system using an electronic fuel injection method employing the thermal flow meter of this embodiment.

[0015] Figure 2 This is the front view of the thermal flow meter in this embodiment.

[0016] Figure 3 It is along Figure 2 The diagram shows a cross-section of the thermal flow meter cut off by line AA.

[0017] Figure 4 From Figure 2 Front view of the circuit board after the casing has been removed.

[0018] Figure 5 From Figure 4 A front view of the circuit board after removing circuit components such as chip packages.

[0019] Figure 6 It is along Figure 5 The diagram shows a cross-section of the circuit board cut by the BB line.

[0020] Figure 7 This is a diagram illustrating a modified example 1 of the circuit board and the conductive coating.

[0021] Figure 8 It is along Figure 7 The diagram shows a cross-section of the circuit board cut by the CC line.

[0022] Figure 9 This is a diagram illustrating a modified example 2 of the circuit board and the conductive coating.

[0023] Figure 10 It is along Figure 9 The diagram shows a cross-section of the circuit board cut by the DD line.

[0024] Figure 11 This is a diagram illustrating a modified example 3 of the circuit board and the conductive coating.

[0025] Figure 12 It is along Figure 11 The diagram shows a cross-section of the circuit board cut by the EE line. Detailed Implementation

[0026] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. Furthermore, components that are given the same reference numerals in each embodiment have the same function in each embodiment unless otherwise specified, and therefore their descriptions are omitted. Additionally, orthogonal coordinate axes are shown in the necessary drawings to clarify the position of each part.

[0027] like Figure 1As shown, the thermal flow meter 20, mounted on a vehicle, is installed on the main passage 22, which serves as the intake passage of the internal combustion engine 10. As described below, the thermal flow meter 20 not only solves the problems listed in the "Problems to be Solved by the Invention" section and achieves the effects listed in the "Effects of the Invention" section, but also fully considers the aforementioned problems, solves various problems required as a product, and achieves various effects. The specific problems solved by the thermal flow meter 20 and the specific effects it achieves are described in the following explanation.

[0028] Figure 2 This is a front view of the thermal flow meter 20 of this embodiment. Figure 2 The image shows the state where the cover 200 has been removed from the housing 100. Figure 3 It is along Figure 2 The diagram shows a cross-sectional view of the thermal flow meter 20 cut by line AA. Figure 4 From Figure 2 A front view of the circuit board 300 after the housing 100 has been removed. In the following description, it is assumed that the measured gas 2 travels along... Figure 1 The flow occurs along the central axis 22a of the main passage 22 shown.

[0029] The thermal flow meter 20 is inserted into the main passage 22 through a mounting hole provided on the passage wall, and is used in a fixed state on the main passage 22. The thermal flow meter 20 has a frame disposed on the main passage 22 through which the measured gas 2 flows. The frame of the thermal flow meter 20 has a housing 100 and a cover 200 mounted on the front of the housing 100.

[0030] The housing 100 is formed, for example, by injection molding of a synthetic resin material.

[0031] The cover 200 is formed, for example, from a plate-like member made of a metallic or synthetic resin material. In this embodiment, it is formed by injection molding of an aluminum alloy or synthetic resin material. The cover 200 has a size that fully covers the front of the housing 100.

[0032] The housing 100 has a flange 111 for securing the thermal flow meter 20 to the main passage 22 and a connector 112 that protrudes from the flange 111 and is exposed to the outside from the main passage 22 for electrical connection with external devices. Furthermore, the housing 100 has a measuring section 113 that extends from the flange 111 toward the central axis 22a of the main passage 22 for measuring the physical quantity of the gas 2 being measured flowing through the main passage 22.

[0033] The measuring section 113 is formed into a thin and long shape that extends straight from the flange 111. The measuring section 113 has a wide front side 121 and a back side 122, a pair of narrow side sides 123 and 124, and a narrow lower surface 125.

[0034] The front surface 121 and the back surface 122 are rectangular surfaces with the long side and short side of the measuring section 113 as its long side and short side, respectively. They are the main surfaces with the largest area among the surfaces constituting the measuring section 113. The front surface 121 and the back surface 122 are arranged parallel to the central axis 22a of the main passage 22 when the thermal flow meter 20 is installed on the main passage 22. The side surface 123 is located on one side of the measuring section 113 in the short side direction and is arranged opposite to the upstream side of the main passage 22 when the thermal flow meter 20 is installed on the main passage 22. The side surface 124 is located on the other side of the measuring section 113 in the short side direction and is arranged opposite to the downstream side of the main passage 22 when the thermal flow meter 20 is installed on the main passage 22. The lower surface 125 is the surface connected to the front surface 121, the back surface 122, the side surface 123, and the side surface 124. The lower surface 125 is located at the top end of the measuring section 113, away from the flange 111, and is arranged parallel to the central axis 22a of the main passage 22 when the thermal flow meter 20 is mounted on the main passage 22. By forming the side surfaces 123 and 124, which are opposite to the upstream and downstream sides of the main passage 22, into a narrow shape, the thermal flow meter 20 can suppress the fluid resistance relative to the measured gas 2 to a small value.

[0035] In this embodiment, the thermal flow meter 20, when mounted on the main passage 22, is positioned such that the base end of the measuring portion 113, which is close to the flange 111, is positioned on the upper side, and the top end of the measuring portion 113, which is away from the flange 111, is positioned on the lower side. However, the posture of the thermal flow meter 20 when mounted on the main passage 22 is not limited to this embodiment and can be various postures. For example, the thermal flow meter 20 can be mounted horizontally with the base end and the top end of the measuring portion 113 at the same height.

[0036] The measuring unit 113 has an inlet 131 for secondary passages 134 and 135 on its side 123, and a first outlet 132 and a second outlet 133 on its side 124. The inlet 131, the first outlet 132, and the second outlet 133 are located at the top end of the measuring unit 113, which extends from the flange 111 toward the central axis 22a of the main passage 22. Therefore, the measuring unit 113 can draw the measured gas 2 flowing in the portion near the central axis 22a of the passage wall away from the main passage 22 into the secondary passages 134 and 135. As a result, the thermal flow meter 20 can measure the flow rate of the measured gas 2 flowing in the portion near the central axis 22a, and can suppress the decrease in measurement accuracy caused by the influence of heat, etc.

[0037] The measuring unit 113 is equipped with a flow detection element 321, an intake temperature sensor 331, and a humidity sensor 333.

[0038] The flow detection element 321 has a diaphragm-like (thin film-like) detection surface 322 and is disposed midway through the secondary passages 134 and 135. The flow detection element 321 detects the flow rate of the gas 2 being measured, i.e., the air flow rate, flowing through the main passage 22. The intake temperature sensor 331 is disposed midway through the temperature detection passage 141, one end of which opens near the inlet 131 provided on the side 123, and the other end opens on both the front 121 and the back 122 of the measuring unit 113. The intake temperature sensor 331 detects the temperature of the gas 2 being measured flowing through the main passage 22. The humidity sensor 333 is disposed in the humidity measuring chamber 142 of the measuring unit 113. The humidity sensor 333 measures the humidity of the gas 2 being measured, which is taken into the humidity measuring chamber 142 from the window 143 opening on the back 122 of the measuring unit 113.

[0039] The measuring section 113 is provided with sub-passage slots 151 and 152 for forming sub-passages 134 and 135 and a circuit chamber 140 for accommodating the circuit board 300.

[0040] The circuit chamber 140 and the secondary passage slots 151 and 152 are recessed in the front surface 121 of the measuring section 113, forming a structure that is covered by the cover 200 installed on the front surface of the housing 100. The circuit chamber 140 is provided in the measuring section 113 in a region near the side surface 123. The secondary passage slots 151 and 152 are provided in the measuring section 113 in regions closer to the lower surface 125 than the circuit chamber 140 and in regions closer to the side surface 124 than the circuit chamber 140.

[0041] The secondary passage slots 151 and 152 form secondary passages 134 and 135 by cooperating with the cover 200 covering the front 121 of the measuring section 113. The secondary passage slots 151 and 152 have a first secondary passage slot 151 and a second secondary passage slot 152.

[0042] The first secondary passage trough 151 is formed such that it extends along the short side of the measuring section 113 between an inlet 131 opening on the side 123 of the measuring section 113 and a first outlet 132 opening on the side 124 of the measuring section 113. The first secondary passage trough 151 forms a first secondary passage 134 in cooperation with the cover 200. The first secondary passage 134 draws in the measured gas 2 flowing through the main passage 22 from the inlet 131 and returns the drawn-in measured gas 2 to the main passage 22 from the first outlet 132. The first secondary passage 134 has a flow path that extends from the inlet 131 along the flow direction of the measured gas 2 in the main passage 22 and connects to the first outlet 132.

[0043] The second secondary passageway 152 branches off midway from the first secondary passageway 151, bends toward the base end of the measuring section 113 (towards the flange 111), and extends along the length of the measuring section 113. Then, the second secondary passageway 152 bends toward the side 124 at the base end of the measuring section 113, and turns back in a U-shape toward the top end of the measuring section 113 (towards the lower surface 125), extending again along the length of the measuring section 113. Furthermore, the second secondary passageway 152 bends toward the side 124 in front of the first outlet 132 and is continuous with the second outlet 133, which opens at the side 124. The second outlet 133 is disposed opposite to the downstream side of the main passageway 22. The second outlet 133 has an opening area slightly larger than the first outlet 132 and is formed at a position adjacent to the base end of the measuring section 113 than the first outlet 132.

[0044] The second secondary passage 152 cooperates with the cover 200 to form a second secondary passage 135. The second secondary passage 135 allows the measured gas 2, which branches off from the first secondary passage 134, to pass through and return to the main passage 22 from the second outlet 133. The second secondary passage 135 has a reciprocating flow path along the long side of the measuring section 113. That is, the second secondary passage 135 has a destination section 136 that branches off midway from the first secondary passage 134 and extends toward the base end of the measuring section 113 (towards the flange 111), and a return section 137 that turns back at the base end of the measuring section 113 and extends toward the top end of the measuring section 113 (towards the lower surface 125). The destination section 136 branches off midway from the first secondary passage 134 and extends away from the first secondary passage 134. The return section 137 turns back at the end of the destination section 136 and extends toward the first secondary passage 134. The return section 137 has a flow path connected to a second outlet 133 that opens toward the downstream side of the main passage 22, located downstream of the inlet 131.

[0045] The second auxiliary passage 135 has a flow detection element 321 disposed midway through the outgoing passage 136. The second auxiliary passage 135 is formed in a reciprocating manner extending along the length direction of the measuring section 113, thus ensuring a longer passage length and reducing the impact on the flow detection element 321 in the event of pulsation within the main passage 22. The flow detection element 321 is disposed on a chip package 310, which is mounted on the circuit board 300. The chip package 310 serves as a support for the flow detection element 321.

[0046] In this embodiment, an example of a chip package 310 sealed with resin to support the flow sensing element 321 is shown, which exposes at least the detection surface 322 (thin-wall portion) of the flow sensing element 321, but is not limited thereto. The chip package 310 can integrally form a throttling shape when the flow sensing element 321 is sealed with resin, thus reducing the deviation in positional relationship between the flow sensing element 321 and the throttling shape, and has the advantage of improving the accuracy of flow detection.

[0047] The circuit board 300 has circuit components such as a chip package 310, a suction temperature sensor 331, a humidity sensor 333, and a pressure sensor 335 mounted on its mounting surface 300a. The suction temperature sensor 331, humidity sensor 333, and pressure sensor 335 are not essential; various sensors can be selected as needed. The circuit board 300 has a roughly rectangular shape when viewed from above. Figure 2 As shown, the circuit board 300 is arranged in the measuring section 113 such that the long side of the circuit board 300 extends from the base end of the measuring section 113 toward the top end, and the short side of the circuit board 300 extends from the side 123 of the measuring section 113 toward the side 124.

[0048] like Figure 4 As shown, the circuit board 300 has a main body 301 disposed in the circuit chamber 140; a first protrusion 302 disposed in the temperature detection passage 141; a second protrusion 303 disposed in the humidity measurement chamber 142; and a third protrusion 304 disposed in the outlet portion 136 of the second secondary passage 135. A pressure sensor 335 and a chip package 310 are mounted on the main body 301, an intake temperature sensor 331 is mounted on the top of the first protrusion 302, and a humidity sensor 333 is mounted on the second protrusion 303.

[0049] The third protrusion 304 is provided to protrude from the circuit chamber 140 toward the sub-passage grooves 151 and 152. Specifically, the third protrusion 304 is provided to extend from the main body portion 301 disposed in the circuit chamber 140 toward the destination portion 136 of the second sub-passage 135. The third protrusion 304 has a facing portion 305 that faces the detection surface 322 of the flow detection element 321 disposed on the chip package 310. In other words, the facing portion 305 is formed by the third protrusion 304 of the circuit board 300.

[0050] like Figure 3As shown, the chip package 310 has a resin package structure formed by molding a flow sensing element 321, an LSI 324, and a lead frame 325 using a resin component 326. The flow sensing element 321 and the LSI 324 are mounted on the lead frame 325. The resin component 326 seals the lead frame 325, which houses the flow sensing element 321 and the LSI 324, with the diaphragm-like sensing surface 322 of the flow sensing element 321 exposed.

[0051] The chip package 310 is formed into a rectangular flat plate shape with a specified thickness. The chip package 310 has a front side 310a opposite to the cover 200 and a back side 310b, which is the side opposite to the front side 310a in the thickness direction of the chip package 310. The front side 310a and the back side 310b of the chip package 310 are large main surfaces that are along the mounting surface 300a of the circuit board 300.

[0052] like Figure 3 and Figure 4 As shown, the chip package 310 has a fixing portion 311 fixed to the main body portion 301 of the circuit board 300 in the circuit chamber 140 and an extension portion 312 extending from the fixing portion 311 toward the second secondary passage 135.

[0053] A plurality of terminals 313 are provided on the fixing portion 311 of the chip package 310. The terminals 313 protrude from both ends of the fixing portion 311 in the width direction along the width direction of the fixing portion 311 in mutually opposite directions. The tip of each terminal 313 is bent in the thickness direction of the fixing portion 311 and positioned to protrude beyond the back surface 310b of the fixing portion 311. The fixing portion 311 of the chip package 310 is fixed to the main body 301 of the circuit board 300 by joining the tip of the terminals 313 to the mounting surface 300a of the main body 301 of the circuit board 300 using soldering or the like. The fixing portion 311 of the chip package 310 is fixed such that a gap is formed between the back surface 310b of the fixing portion 311 and the mounting surface 300a of the main body 301 of the circuit board 300 in the thickness direction of the fixing portion 311.

[0054] The protrusion 312 of the chip package 310 is disposed opposite to the third protrusion 304 (opposing portion 305) of the circuit board 300 in the destination portion 136 of the second secondary passage 135. A groove 314 is formed on the protrusion 312 of the chip package 310, recessed from the back side 310b of the protrusion 312 toward the front side 310a. The groove 314 is formed on the back side 310b of the protrusion 312 and extends in the entire width direction of the protrusion 312. At the middle position of the direction in which the groove 314 extends, the detection surface 322 of the flow detection element 321 is exposed.

[0055] The chip package 310 is configured such that a recess 314 extends along the destination portion 136 of the second sub-passage 135. The chip package 310 is configured such that the detection surface 322 of the flow sensing element 321 faces the third protrusion 304 (opposing portion 305), which is part of the circuit board 300. A passage P is formed between the recess 314 of the protrusion 312 and the third protrusion 304 (opposing portion 305) of the circuit board 300. That is, the recess 314 cooperates with the third protrusion 304 (opposing portion 305) to form the passage P. The passage P is part of the destination portion 136 of the second sub-passage 135 through which the measured gas 2 flows. The measured gas 2 flowing through the second sub-passage 135 passes through the passage P, and the detection surface 322 of the flow sensing element 321 is exposed.

[0056] The flow sensing element 321 has a sensing surface 322 with a pair of temperature sensor resistors and a heater to acquire changes in the temperature distribution of the gas 2 being measured along the direction of passage P. Based on the changes in temperature distribution acquired by the sensing surface 322, the flow sensing element 321 detects the flow rate of the gas 2 being measured through passage P. Thus, the thermal flow meter 20 can measure the flow rate of the intake air, which is the gas 2 being measured, drawn from the main passage 22 into the secondary passages 134 and 135, and output a signal indicating the measurement result to the control device 4.

[0057] The intake air, which is the gas being measured 2, sometimes contains impurities such as dust, oil, or carbon. Although most of the impurities such as dust are removed by the air filter 21, sometimes a small amount of impurities composed of microparticles are taken into the secondary passages 134 and 135 through the air filter 21. It is known that impurities composed of microparticles generate charge movement through mutual collisions, for example, becoming positively charged.

[0058] If the measured gas 2 containing charged impurities is continuously introduced into the secondary passages 134 and 135, the charged impurities may accumulate on the detection surface 322 of the flow sensing element 321 located in the secondary passages 134 and 135. When impurities accumulate on the detection surface 322, the flow sensing element 321 may not be able to properly detect the temperature distribution of the measured gas 2, and therefore may not be able to properly detect the flow rate of the measured gas 2. Therefore, it is important to prevent charged impurities from accumulating on the detection surface 322.

[0059] One method to reduce the accumulation of charged impurities on the detection surface 322 is to add a de-energizing function to the thermal flow meter 20 to neutralize the charged impurities contained in the measured gas 2, thereby reducing the accumulation of impurities on the detection surface 322. This de-energizing function sets the potential of the opposite portion 305 of the circuit board 300 that forms the exposed passage P of the detection surface 322 to a potential capable of de-energizing the charged impurities. This de-energizing function only requires that the opposite portion 305 of the circuit board 300 be conductive, but it is more preferable that it have a predetermined potential. This is because due to the Coulomb force generated between the charged impurities and the opposite portion 305 that performs the de-energizing function, the charged impurities easily come into contact with the opposite portion 305, promoting the neutralization of the charged impurities. Examples of predetermined potentials include power supply potential or ground potential.

[0060] This power-removing function can be achieved, for example, by exposing a wiring pattern having the ground potential of the circuit board 300 on the mounting surface 300a of the circuit board 300 on the opposite portion 305 of the circuit board 300. The wiring pattern of the circuit board 300 is usually formed of an easily corroded metal foil such as copper foil, so from the viewpoint of preventing corrosion, electroplating is performed.

[0061] Since the thermal flow meter 20 is used in vehicles and other products requiring high reliability, it is necessary to perform multi-layer electroplating on the wiring pattern exposed on the mounting surface 300a of the circuit board 300. For example, if the wiring pattern exposed on the mounting surface 300a of the circuit board 300 is copper foil, electroless Ni plating is performed on the wiring pattern, followed by electroless Pd plating, and then electroless Au replacement plating. Performing such multi-layer electroplating on the wiring pattern exposed on the surface of the circuit board 300 is a major reason for the significant increase in the cost of the thermal flow meter 20.

[0062] Furthermore, the wiring pattern exposed on the mounting surface 300a of the circuit board 300 is typically surrounded by an insulating film such as solder resist from the direction along the mounting surface 300a of the circuit board 300. Therefore, even if electroplating is performed on the wiring pattern exposed on the mounting surface 300a of the circuit board 300, the electroplating only covers the upper surface of the wiring pattern, and it is difficult to completely cover the side surface of the wiring pattern adjacent to the insulating film such as solder resist. Especially when electroless Ni plating is performed, there is a high possibility that the electroless Ni plating will be exposed from the side surface of the wiring pattern, and the electroless Ni plating will corrode. If the electroless Ni plating corrodes, the wiring pattern of the circuit board 300 is also prone to corrosion, so the potential of the opposite portion 305 of the circuit board 300 cannot be properly stabilized, which may affect the removal function of impurities. As a result, in the thermal flow meter 20, charged impurities may easily accumulate on the detection surface 322. Consequently, in the thermal flow meter 20, it may not be able to properly detect the flow rate of the measured gas 2 for a long period of time.

[0063] In the thermal flow meter 20 of this embodiment, by sealing the second conductor portion 309, which is a wiring pattern exposed on the mounting surface 300a of the circuit board 300, with the conductive coating 400 described below, the function of removing impurities can be reliably realized even at low cost, thus achieving a long service life.

[0064] Figure 5 From Figure 4 A front view of the circuit board 300 after removing circuit components such as the chip package 310. Figure 6 It is along Figure 5 The diagram shows a cross-section of the circuit board 300 cut by the BB line.

[0065] like Figure 6 As shown, the circuit board 300 has a multilayer structure in which insulating portions 306 and 307 and conductor portions 308 and 309 are stacked.

[0066] Insulating portions 306 and 307 include a first insulating portion 306, which is provided as an inner layer of the circuit board 300 and is made of an insulating substrate such as a glass epoxy board or a paper phenolic substrate, and a second insulating portion 307, which is provided as the outermost layer of the circuit board 300 and is made of an insulating film such as a solder resist. The first insulating portion 306 holds conductor portions 308 and 309, which are provided as an inner layer of the circuit board 300. The second insulating portion 307 surrounds the conductor portions 308 and 309, which are provided as the outermost layer of the circuit board 300, from the direction along the mounting surface 300a of the circuit board 300.

[0067] Conductor portions 308 and 309 are wiring patterns formed from metal foil such as copper foil. Conductor portions 308 and 309 include a first conductor portion 308 having a potential other than the ground potential of the circuit board 300, and a second conductor portion 309 having a ground potential. The ground potential of the circuit board 300 can be a potential capable of removing charged impurities contained in the measured gas 2. When the potential of the charged impurities is positive, the ground potential of the circuit board 300 can also be negative.

[0068] The first conductor portion 308 includes Figure 6 The wiring pattern shown is provided as an internal layer of the circuit board 300. Figure 5 The wiring pattern shown is provided as the outermost layer of the circuit board 300. The wiring pattern formed as the outermost layer of the circuit board 300 is, for example, a wiring pattern of metal pads that are bonded to the terminals 313 of the chip package 310. The first conductor portion 308 is continuously provided on the main body portion 301, the first protrusion 302, the second protrusion 303 and the third protrusion 304 of the circuit board 300.

[0069] The second conductor portion 309 is a wiring pattern that is connected to the ground wiring pattern of the circuit board 300. That is, the second conductor portion 309 has the ground potential of the circuit board 300. The second conductor portion 309 is provided as the outermost layer of the circuit board 300. The second conductor portion 309 is the portion exposed from the insulating portions 306 and 307 of the circuit board 300 to the mounting surface 300a of the circuit board 300. The second conductor portion 309 is provided on the opposing portion 305 (third protrusion 304) of the circuit board 300 opposite to the detection surface 322 of the flow detection element 321.

[0070] like Figure 5 As shown, the second conductor portion 309 is formed in a rectangular shape along the mounting surface 300a of the circuit board 300. The second conductor portion 309 is formed to extend along the direction of the destination portion 136 of the second sub-passage 135 and the width direction of the destination portion 136 of the second sub-passage 135. That is, the second conductor portion 309 is formed to extend along the direction of the passage P formed by the recess 314 of the chip package 310 and the width direction of the passage P.

[0071] The second conductor portion 309 is disposed facing the interior of the passage P, which is part of the destination portion 136 of the second sub-passage 135 through which the measured gas 2 flows, with the conductive coating film 400 in between. The second conductor portion 309 is disposed in a manner that blocks the interior of the passage P from the circuit board 300 side in the opposing portion 305 of the circuit board 300. The second conductor portion 309 is disposed in a manner that spans across the passage P in the width direction. The second conductor portion 309 is disposed in a manner that exceeds the width of the passage P and extends to a portion 312a closer to the circuit chamber 140 side than the passage P of the protrusion portion 312. In other words, the second conductor portion 309 is disposed in a manner that the length W1 along the width of the second sub-passage 135, that is, the length W1 along the width of the passage P, is longer than the width W3 of the passage P and the width W4 of the destination portion 136 of the second sub-passage 135. However, the length W1 of the second conductor portion 309 along the width of the passage P is preferably provided to be greater than or equal to the width W2 of the detection surface 322 of the flow detection element 321 in the passage P, but there is no particular limitation.

[0072] The conductive coating 400 is an example of a conductive resin component comprising a conductive material and a resin, which is coated onto a circuit board 300 and formed into a film. The conductive material comprising the conductive coating 400 can be, for example, a metal such as carbon, silver, copper, or aluminum, or a metal oxide such as tin oxide, indium tin oxide (ITO), or antimony-doped tin oxide (ATO). The resin comprising the conductive coating 400 can be, for example, an epoxy resin, phenolic resin, fluororesin, or polyester resin, which has adhesive properties to the circuit board 300. From the viewpoint of improving corrosion resistance, the conductive material comprising the conductive coating 400 is preferably carbon; from the viewpoint of improving chemical resistance and heat resistance, the resin comprising the conductive coating 400 is preferably epoxy resin or phenolic resin. Furthermore, from the viewpoint of improving heat resistance, epoxy resin is more preferably the resin comprising the conductive coating 400.

[0073] The conductive coating 400 is easily bonded to the circuit board 300 by printing or spraying, followed by drying and curing in a constant temperature bath. The bonding process of the conductive coating 400 to the circuit board 300 is simpler and less expensive than electroplating. The material cost of the conductive coating 400 is also lower than that of electroplating.

[0074] like Figure 5 As shown, a conductive coating 400 is disposed on the opposing portion 305 of the circuit board 300 opposite to the detection surface 322 of the flow detection element 321. The conductive coating 400 seals the second conductor portion 309 disposed on the opposing portion 305 of the detection surface 322. That is, the conductive coating 400 seals the second conductor portion 309 disposed on the third protrusion 304 constituting the opposing portion 305. Specifically, as... Figure 6 As shown, the conductive coating 400 covers without gaps the upper surface 309a opposite to the detection surface 322 of the second conductor portion 309 and the side surface 309b connected to the upper surface 309a of the second conductor portion 309. Thus, the conductive coating 400 can seal the second conductor portion 309, which is a wiring pattern exposed on the mounting surface 300a of the circuit board 300. The conductive coating 400 is in contact with the second conductor portion 309 having the ground potential of the circuit board 300 and has the same ground potential as the second conductor portion 309.

[0075] The conductive coating 400 is disposed in the opposing portion 305 of the circuit board 300, facing the interior of the passage P, which is part of the outlet portion 136 of the second sub-passage 135 through which the measured gas 2 flows. The conductive coating 400 seals the second conductor portion 309 disposed in a manner that blocks the interior of the passage P from the circuit board 300 side. The conductive coating 400 seals the second conductor portion 309 disposed in a manner that spans across the passage P in the width direction. The conductive coating 400 seals the second conductor portion 309 disposed in a manner that exceeds the width of the passage P and extends to the portion 312a of the circuit chamber 140 closer than the passage P of the protrusion 312. In other words, the conductive coating 400 is configured such that the length W along the width of the second sub-passage 135, that is, the length W along the width of the passage P, is longer than the length W1 along the width of the passage P of the second conductor portion 309. Preferably, the conductive coating 400 is arranged such that the length W along the width of the passage P is longer than the width W3 of the passage P and the width W4 of the outlet portion 136 of the second sub-passage 135.

[0076] The conductive coating 400 contacts the second insulating portion 307 surrounding the second conductor portion 309 from the direction along the mounting surface 300a of the circuit board 300, sealing the second conductor portion 309. Specifically, the conductive coating 400 contacts at least one of the upper surface 307a opposite to the detection surface 322 and the side surface 307b connected to the upper surface 307a of the second insulating portion 307 adjacent to the second conductor portion 309 in the direction along the mounting surface 300a of the circuit board 300, sealing the second conductor portion 309.

[0077] In the thermal flow meter 20 of this embodiment, the detection surface 322 of the flow detection element 321 and a portion of the circuit board 300 are arranged opposite each other. A conductive member is provided on at least a portion of the opposing portion 305 within the second secondary passage 135 on the surface opposite to the detection surface 322 of the circuit board 300. The thermal flow meter 20 achieves the static elimination function on the circuit board 300 using a conductive resin member with higher corrosion resistance than electroplating, thus enabling long service life even at low cost and ensuring reliable flow detection accuracy.

[0078] In the thermal flow meter 20, the conductive resin component that performs the static elimination function is preferably a conductive coating 400 formed by coating the circuit board 300 into a film. Therefore, the static elimination function can be achieved in the thermal flow meter 20 with a simple process, thus further reducing costs.

[0079] Furthermore, in the thermal flow meter 20, the support body for supporting the flow sensing element 321 is mounted on the circuit board 300 as a chip package 310, and the sensing surface 322 of the flow sensing element 321 and the circuit board 300 are arranged opposite each other, thereby forming a path P as a flow sensing path. Therefore, in the thermal flow meter 20, since the influence of the housing 100, cover 200, and circuit board 300 can be eliminated from the main causes of installation deviation in the path P as a flow sensing path, the reliability of flow sensing accuracy can be improved.

[0080] Furthermore, in the thermal flow meter 20, when the conductive coating 400, which is a conductive resin component provided on the circuit board 300, is at a predetermined potential, even if the measured gas 2 containing charged impurities flows to the flow detection element 321, the charged impurities can be attracted to the conductive coating 400 by Coulomb force and moved away from the flow detection element 321. In addition, in the thermal flow meter 20, the conductive coating 400 can de-charge after attracting charged impurities, thus further suppressing impurity accumulation on the detection surface 322 of the flow detection element 321.

[0081] The conductive coating 400 is provided in a manner that overlaps with the exposed portion (second conductor portion 309) of the wiring on the circuit board 300, thereby enabling the conductive coating 400 to reach a predetermined potential. The predetermined potential can be ground potential or power supply potential. Since most impurities passing through the air filter 21 are positively charged, it is more preferable to use the second conductor portion 309 covered by the conductive coating 400 as ground wiring and the conductive coating 400 as ground potential. Furthermore, by overlapping the conductive coating 400 with the second conductor portion 309, it is advantageous to form a static elimination function with a simple configuration. When it is desired to form a static elimination function on a component such as the cover 200 where no signal lines are provided, a complex mechanism for connecting the circuit board 300 and the cover 200 is required to connect to the predetermined potential. In contrast, by forming a film by coating a conductive resin component on a portion of the circuit board 300 in a manner that covers wiring at the predetermined potential, a static elimination function with a predetermined potential can be easily achieved.

[0082] Furthermore, in the thermal flow meter 20, the opposing portion 305 opposite to the flow detection element 321 of the circuit board 300 is composed of a third protrusion 304 protruding into the second secondary passage 135. Moreover, in the thermal flow meter 20, it is preferable that a second conductor portion 309 is provided on the third protrusion 304, and a conductive coating 400 seals the second conductor portion 309 on the third protrusion 304.

[0083] With the above configuration, in the thermal flow meter 20, the second conductor portion 309, which serves as the potential supply source for de-energizing charged impurities, is positioned facing the interior of the second secondary passage 135 through which the measured gas 2 flows, separated by a conductive coating film 400. In the thermal flow meter 20, the conductive coating film 400 facing the interior of the second secondary passage 135 through which the measured gas 2 flows is extremely close to the second conductor portion 309, allowing the charge supplied from the second conductor portion 309 to the conductive coating film 400 to immediately diffuse across the entire surface of the conductive coating film 400. In the thermal flow meter 20, the potential of the conductive coating film 400 facing the interior of the second secondary passage 135 and the second conductor portion 309 can immediately become the same potential, thus enabling the de-energizing function of impurities to operate immediately. As a result, in the thermal flow meter 20, the accumulation of impurities on the detection surface 322 can be further suppressed.

[0084] Furthermore, in the thermal flow meter 20, the length W1 of the second conductor portion 309 along the width of the second secondary passage 135 is greater than or equal to the width W4 of the second secondary passage 135, and the length W of the conductive coating film 400 along the width of the second secondary passage 135 is longer than the length W1 of the second conductor portion 309. That is, in the thermal flow meter 20, it is preferable that both the length W of the conductive coating film 400 and the length W1 of the second conductor portion 309 are greater than or equal to the width W4 of the second secondary passage 135.

[0085] With the above configuration, in the thermal flow meter 20, the potential of the conductive coating 400 facing the interior of the second sub-passage 135 through which the measured gas 2 flows can be easily and uniformly distributed along the entire width of the second sub-passage 135. In the thermal flow meter 20, deviations in the removal function of impurities along the width of the second sub-passage 135 can be suppressed. Furthermore, in the thermal flow meter 20, since the surface of the conductive coating 400 facing the interior of the second sub-passage 135 can be smoothly maintained, the measured gas 2 can flow stably, thus enabling high-precision detection of the flow rate of the measured gas 2. In the thermal flow meter 20, reducing the accumulation of impurities on the detection surface 322 not only allows for long-term, accurate detection of the flow rate of the measured gas 2 but also improves the accuracy of flow rate detection. Therefore, the thermal flow meter 20 can achieve a long service life and improved detection accuracy even at low cost.

[0086] Furthermore, in the thermal flow meter 20, it is preferable that the conductive coating 400 contacts the second insulating portion 307 surrounding the second conductor portion 309 from the direction along the mounting surface 300a of the circuit board 300, thereby sealing the second conductor portion 309.

[0087] With the above-described configuration, in the thermal flow meter 20, the conductive coating 400 reliably seals the second conductor portion 309 and improves the adhesion between the conductive coating 400 and the circuit board 300, thus further extending the lifespan of the impurity removal function. In the thermal flow meter 20, the accumulation of impurities on the detection surface 322 can be further reduced, enabling more accurate detection of the flow rate of the measured gas 2 for a longer period. Therefore, the thermal flow meter 20 can achieve a longer lifespan even at a low cost.

[0088] Furthermore, in the thermal flow meter 20, the conductive material that constitutes the conductive coating 400 is preferably carbon with high corrosion resistance, and the resin that constitutes the conductive coating 400 is epoxy resin or phenolic resin with high chemical resistance and heat resistance.

[0089] Through the above-described configuration, the thermal flow meter 20 improves the corrosion resistance, chemical resistance, and heat resistance of the conductive coating 400, thereby extending the lifespan of its impurity removal function. The thermal flow meter 20 also further reduces impurity accumulation on the detection surface 322, enabling more accurate and prolonged detection of the flow rate of the measured gas 2. Thus, the thermal flow meter 20 can achieve a longer lifespan even at a lower cost.

[0090] [Examples of Modification of Circuit Board and Conductive Coating]

[0091] Figure 7 This is a diagram illustrating a modified example 1 of the circuit board 300 and the conductive coating 400. Figure 7 Corresponding to Figure 5 . Figure 8 It is along Figure 7 The diagram shows a cross-section of the circuit board 300 cut by the CC line. Figure 8 Corresponding to Figure 6 .

[0092] exist Figure 5 and Figure 6 In the circuit board 300 shown, the second conductor portion 309 is disposed such that it faces the interior of the passage P, which is part of the destination portion 136 of the second secondary passage 135 through which the measured gas 2 flows, with the conductive coating 400 in between. In contrast, in Figure 7 and Figure 8 In the circuit board 300 shown, the second conductor portion 309 may not be arranged so that it faces the interior of the passage P, which is part of the destination portion 136 of the second sub-passage 135, through the conductive coating 400. Figure 7 and Figure 8 The conductive coating 400 shown is... Figure 5 and Figure 6Similarly, the conductive coating 400 shown is arranged so that it faces the interior of the passage P, which is part of the destination portion 136 of the second sub-passage 135.

[0093] exist Figure 7 and Figure 8 In the thermal flow meter 20 of the modified example 1 shown, even if the second conductor portion 309 faces the interior of the passage P without being separated by the conductive coating 400, the removal of impurities can be reliably achieved even at low cost because the conductive coating 400 faces the interior of the passage P.

[0094] In addition, Figure 5 and Figure 6 In the circuit board 300 shown, the size of the second conductor portion 309 is slightly smaller than the size of the conductive coating film 400, but the difference in size between the two is not significant. In contrast, in... Figure 7 and Figure 8 In the circuit board 300 shown, the size of the second conductor portion 309 can also be significantly smaller than the size of the conductive coating 400. For example, in Figure 5 and Figure 6 In the circuit board 300 shown, the length W1 of the second conductor portion 309 is greater than or equal to the width W4 of the second sub-pass 135, while... Figure 7 and Figure 8 In the circuit board 300 shown, the length W1 of the second conductor portion 309 can be less than the width W4 of the second secondary passage 135. Figure 7 and Figure 8 In the conductive coating 400 shown, with Figure 5 and Figure 6 Similarly, the conductive coating 400 shown has a length W along the width of the second sub-path 135 that is greater than or equal to the width W4 of the second sub-path 135.

[0095] Figure 7 and Figure 8 In the modified example 1, the size of the second conductor portion 309 of the thermal flow meter 20 is significantly smaller than the size of the conductive coating 400. Therefore, the conductive coating 400 can reliably seal the second conductor portion 309 and improve the adhesion to the circuit board 300. Furthermore, Figure 7 and Figure 8 The thermal flow meter 20 of Modified Example 1 shown can reduce the amount of the second conductor portion 309 formed from relatively expensive materials such as copper foil, thus reducing material costs. Therefore, Figure 7 and Figure 8 The thermal flow meter 20 of Modified Example 1 shown can further reduce costs and extend the lifespan of the impurity removal function. Therefore, in Figure 7 and Figure 8In the thermal flow meter 20 of the modified example 1 shown, the cost can be further reduced, and even with low cost, the service life can be further extended.

[0096] Figure 9 This is a diagram illustrating a modified example 2 of the circuit board 300 and the conductive coating 400. Figure 9 Corresponding to Figure 7 . Figure 10 It is along Figure 9 The diagram shows a cross-section of the circuit board 300 cut by the DD line. Figure 10 Corresponding to Figure 8 .

[0097] exist Figure 7 and Figure 8 In the circuit board 300 shown, the second conductor portion 309 is formed of a metal foil, such as copper foil, which is significantly smaller in size than the conductive coating 400. In contrast, in... Figure 9 and Figure 10 In the circuit board 300 shown, the second conductor portion 309 may also be formed by a through hole. The second conductor portion 309 formed by the through hole is in communication with the ground wiring pattern 309' provided as a layer inside the circuit board 300.

[0098] Figure 9 and Figure 10 The thermal flow meter 20 shown in Modified Example 2 is... Figure 7 and Figure 8 Similarly, the thermal flow meter 20 of Modified Example 1 shown can reduce costs and extend the lifespan of the impurity removal function. Therefore, in Figure 9 and Figure 10 In the thermal flow meter 20 of the modified example 2 shown, a long service life can be achieved even at low cost.

[0099] Figure 11 This is a diagram illustrating a modified example 3 of the circuit board 300 and the conductive coating 400. Figure 11 Corresponding to Figure 7 . Figure 12 It is along Figure 11 The diagram shows a cross-section of the circuit board 300 cut by the EE line. Figure 12 Corresponding to Figure 8 .

[0100] exist Figure 7 and Figure 8 In the circuit board 300 shown, the second conductor portion 309 is provided on the third protrusion 304 of the circuit board 300. Figure 7 and Figure 8 The conductive coating 400 shown seals the second conductor portion 309 on the third protrusion 304. In contrast, in Figure 11 and Figure 12 In the circuit board 300 shown, the second conductor portion 309 may also be provided on the main body portion 301 of the circuit board 300. Figure 11 and Figure 12 The conductive coating 400 shown can also be provided from the third protrusion 304 of the circuit board 300 to the main body 301, sealing the second conductor portion 309 provided on the main body 301.

[0101] exist Figure 11 and Figure 12 In the thermal flow meter 20 of the modified example 3 shown, since the second conductor portion 309 is located on the main body portion 301 away from the passage P, the heat of the second conductor portion 309 is difficult to transfer to the measured gas 2 flowing through the passage P. Figure 11 and Figure 12 In the thermal flow meter 20 of Modified Example 3 shown, the temperature distribution of the measured gas 2 obtained on the detection surface 322 is less affected by the heat of the second conductor portion 309, thus enabling more accurate detection of the flow rate of the measured gas 2. Therefore, in Figure 11 and Figure 12 In the thermal flow meter 20 of the modified example 3 shown, a long service life can be achieved even at low cost, and the detection accuracy can be improved.

[0102] In the above embodiment, the case where the second conductor portion 309 has the ground potential of the circuit board 300 was described as an example. However, the second conductor portion 309 only needs to have a potential capable of de-energizing charged impurities, and it may also have a potential other than the ground potential of the circuit board 300. In this case, the second conductor portion 309 can simply be a conductor portion such as a wiring pattern exposed from the insulating portions 306 and 307 of the circuit board 300 to the mounting surface 300a, and it can be insulated from the wiring pattern having the ground potential of the circuit board 300.

[0103] [other]

[0104] Furthermore, the present invention is not limited to the embodiments described above, but also includes various modifications. For example, the above-described embodiments are detailed for the purpose of easily understanding and explaining the present invention, and are not necessarily limited to having all the described configurations. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Furthermore, for a part of the configuration of each embodiment, other configurations can be added, deleted, or replaced.

[0105] Furthermore, the aforementioned components, functions, processing units, and processing modules can also be implemented in hardware, for example, by designing some or all of them using integrated circuits. Alternatively, the aforementioned components and functions can be implemented in software by a processor interpreting and executing programs that perform their respective functions. The programs implementing these functions, magnetic tapes, files, and other information can be stored in recording devices such as memory, hard disks, SSDs (solid-state drives), or recording media such as IC cards, SD cards, and DVDs.

[0106] Furthermore, while the designation of control lines and information lines is considered necessary in the specifications, it is not necessarily true that all control lines and information lines are represented on the product itself. In reality, it can be assumed that almost all components are interconnected.

[0107] Symbol Explanation

[0108] 2…Measured gas, 20…Thermal flow meter, 22…Main passage, 135…Second auxiliary passage, 140…Circuit chamber, 300…Circuit board, 301…Main body, 304…Third protrusion, 305…Opposite part, 307…Second insulating part, 309…Second conductor part, 310…Chip package, 321…Flow detection element, 322…Detection surface, 400…Conductive coating.

Claims

1. A thermal flow meter, characterized in that, have: Flow detection element, which detects air flow; and A circuit board, which is arranged such that a portion of it faces the detection surface of the flow detection element. The circuit board has a conductive resin component comprising conductive material and resin on at least a portion of the surface opposite to the detection surface of the flow detection element and disposed within the secondary passage. The conductive resin component is formed as a conductive film by coating it onto the circuit board. The conductive coating is provided in such a way that it seals the conductor portion formed on the circuit board at a specified potential.

2. The thermal flow meter according to claim 1, characterized in that, The circuit board also includes wiring and an insulating film disposed to cover the wiring. The conductor portion is the part exposed from the insulating film of the wiring.

3. The thermal flow meter according to claim 1 or 2, characterized in that, It also includes a circuit chamber adjacent to the secondary passage and housing the circuit board. The secondary passage is a passage that takes in a portion of the gas being measured flowing in the main passage. The circuit board has a main body disposed in the circuit chamber and a protrusion protruding from the circuit chamber toward the secondary passage. The conductor portion is disposed on the protrusion. The conductive coating is applied to the protrusion.

4. The thermal flow meter according to claim 3, characterized in that, The length of the conductor portion along the width of the secondary passage is greater than or equal to the width of the secondary passage. The length of the conductive coating along the width of the secondary pathway is longer than the length of the conductor portion along the width of the secondary pathway.

5. The thermal flow meter according to claim 3, characterized in that, The length of the conductor portion along the width of the secondary passage is less than the width of the secondary passage. The length of the conductive coating along the width of the sub-path is greater than or equal to the width of the sub-path.

6. The thermal flow meter according to claim 1 or 2, characterized in that, It also includes a circuit chamber adjacent to the secondary passage and housing the circuit board. The secondary passage is a passage that takes in a portion of the gas being measured flowing in the main passage. The circuit board has a main body disposed in the circuit chamber and a protrusion protruding from the circuit chamber to the secondary passage. The conductor portion is disposed on the main body portion. The conductive coating is applied from the protrusion to the main body.

7. The thermal flow meter according to claim 1, characterized in that, The specified potential is the grounding potential.

8. The thermal flow meter according to claim 1, characterized in that, The conductive material is carbon. The resin is epoxy resin or phenolic resin.

9. The thermal flow meter according to claim 1 or 2, characterized in that, It also includes a support body for supporting the flow detection element. The support is mounted on the circuit board with the detection surface of the detection element facing a portion of the circuit board.

10. The thermal flow meter according to claim 9, characterized in that, The support is a chip package formed by sealing it with resin in a manner that exposes at least the detection surface of the flow sensing element.

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