Sensor components

Abstract

We disclose herein a flow sensor assembly comprising a first substrate, a flow sensor positioned on the first substrate, a cover positioned above the flow sensor, an inlet flow channel, and an outlet flow channel. A surface of the flow sensor and a surface of the cover cooperate to form a flow sensing channel between the inlet flow channel and the outlet flow channel, and the surface of the flow sensing channel is substantially flat along the entire length of the flow sensing channel.

Description

Technical Field

[0001] The present disclosure relates to a fluid flow sensor assembly and, in particular, but not exclusively, to a miniaturized fluid flow sensor assembly having reduced turbulence and that can be manufactured in very high volumes at a low unit cost. Background Art

[0002] Thermal fluid flow sensors utilize the thermal interaction between the sensor itself and the fluid. Depending on the physical phenomena governing the interaction, flow sensors can be divided into the following three categories:

[0003] (i) an air velocity sensor for measuring convective heat transfer caused by the flow of fluid past the heating element;

[0004] (ii) a calorimetric sensor for detecting an asymmetry in the temperature profile produced by the heating element and resulting from forced convection of the fluid flow; and

[0005] (iii) Time of Flight (ToF) sensors, used to measure the time elapsed between the sensing and application of a heat pulse.

[0006] Reviews of thermal fluid flow sensors have been published in (B. Van Oudheusden, "Silicon flowsensors," in Control Theory and Applications, IEE Proceedings D, 1988, pp. 373-380); B. Van Oudheusden, "Silicon thermal flow sensors," Sensors and Actuators A: Physical, vol. 30, pp. 5-26, 1992; N. Nguyen, "Micromachined flow sensors—A review," Flow measurement and Instrumentation, vol. 8, pp. 7-16, 1997; Y.-H. Wang et al. al. (N. Nguyen, “Micromachined Flow Sensors—A Review,” Flow Measurement and Instrumentation, vol. 8, pp. 7-16, 1997; Y.-H. Wang et al.), “MEMS-based gas flow sensors,” Microfluidics and nanofluidics, vol. 6, pp. 333-346, 2009; J.T. Kuo et al. (“MEMS-based gas flow sensors,” Microfluidics and Nanofluidics, vol. 6, pp. 333-346, 2009; J.T. Kuo et al.), “Micromachined Thermal Flow Sensors—A Review,” Micromachines, vol. 3, pp. 550-573, 2012). Further background information can also be found in US Pat. No. 6,460,411 to Kersjes et al.

[0007] Typically, a flow sensor assembly consists of a sensing die, a substrate, and a housing. In most cases, the housing includes a flow channel with an inlet and an outlet. The flow channel is the fluidic element responsible for driving the fluid through the sensing die. The design of the flow channel strongly influences the performance of the flow sensing assembly (e.g., range, accuracy, noise, etc.). Some ways to improve flow laminarity, or more generally, better control of the flow, include:

[0008] (i) designing a flow channel that is long enough to achieve a sufficiently extended flow, thus free of turbulence and a well-defined flow profile that is independent of the flow profile at the inlet of the channel;

[0009] (ii) designing a flow channel with a flow restrictor above the sensing surface to increase the flow velocity across the sensor and stimulate the re-expansion of the flow profile;

[0010] (iii) Designing a flow channel with a flow restrictor away from the sensing surface to increase the fluid impedance and have a flow velocity profile (curve) through the sensor that is more independent of the inlet flow profile;

[0011] (iv) Designing flow channels with smooth surfaces and corners to avoid turbulence;

[0012] (v) Design the flow channel with devices (e.g., bends, reservoirs, etc.) to avoid the interaction and accumulation of particles (e.g., dust) on or near the flow sensing surface.

[0013] Electrical connections (e.g., bond wires) to the flow sensing die are often used. These connections can interfere with the fluid flow, creating unwanted turbulence. In addition, the fluid can mechanically and chemically interact with the interconnects, causing them to fail. Precautions can be taken to protect the connections.

[0014] When the flow sensor components have a tiny form factor (e.g., sub-centimeter), implementation of the above approach can prove extremely challenging. This may be because there is insufficient space to physically implement the solution, or the technology to implement the solution is too expensive for products targeting the high-volume, low-cost consumer market.

[0015] Four assembly strategies are used in the prior art, such as Figures 1A to 1D As shown:

[0016] exist Figure 1A wherein the flow sensing die and the electrical connections are exposed to a fluid flow in a flow channel;

[0017] exist Figure 1B wherein a flow sensing region of the flow sensing die is exposed to the fluid flow in the flow channel and the electrical connections are isolated from the flow sensing channel in the secondary volume;

[0018] exist Figure 1C wherein the flow sensing die is assembled to be level with the substrate surface within the cavity in the substrate and electrically connected to be exposed to the fluid flow in the flow channel; and

[0019] exist Figure 1DIn [1], the flow sensing die is partially overmolded in a way that protects the electrical connections. The overmolding used overlaps the substrate. This is an inefficient use of substrate area.

[0020] In US5404753, US8418549, US8695417, US9003877, US9091577, the flow sensor assembly has bond pads spaced away from the sensing structure to allow sufficient space for the wall separating the flow channel from the bond wire cavity. This approach results in a large die size and limits miniaturization of the flow sensor assembly.

[0021] In US10107662B2, US20040118218A1, US20180172493A1 and US4548078, the flow sensing die is located in a cavity so that the surface of the flow sensing die is flush with one of the walls of the flow channel. The presence of such a cavity is detrimental to the flow profile.

[0022] In EP1717562A1, standard forming (molding) technology for general semiconductor packaging is used. However, the forming technology requires high tool costs, and the tools are design-specific. If the design must be changed, new tools are required. In addition, the forming technology requires a certain gap between the edge of the mold and the edge of the flow sensing structure (e.g., a thin film) on the flow sensing surface of the flow sensing die. This imposes limitations on the miniaturization of the sensing die and the final form factor of the flow sensor assembly. In addition, the mold may bleed onto the flow sensing structure, causing the device to become scrap during the inspection stage. Therefore, preventive measures must be taken (e.g., strict control of the forming process, beams or walls on the die surface) to minimize the scrap rate. Preventive measures are usually accompanied by additional process steps and associated risks and costs. Similar considerations apply to US20160161314A1. Summary of the Invention

[0023] Aspects and preferred features are set out in the appended claims.

[0024] According to a first aspect of the present disclosure, a flow sensor assembly is provided, comprising: a first substrate; a flow sensor positioned on the first substrate; a cover positioned above the flow sensor; a flow inlet channel; and a flow outlet channel, wherein a surface of the flow sensor and a surface of the cover cooperate to form a flow sensing channel between the flow inlet channel and the flow outlet channel; and wherein the surface of the flow sensing channel is substantially flat over the entire length of the flow sensing channel.

[0025] The flow sensor assembly provides a miniature fluid flow sensor assembly that can be manufactured in high volume at a low unit cost, thereby reducing the occurrence of turbulence near a flow sensing structure to improve flow sensing performance while maintaining a miniaturized form factor.

[0026] The flow sensing channel can extend laterally through the device, thereby providing a fluid flow path (fluid flow path) that passes laterally through the sensor assembly and through the flow sensor. The inlet channel, the outlet channel and the flow sensing channel together form a flow channel. The flow sensing channel can be defined as the entire length of the portion of the flow channel between the inlet channel and the outlet channel. In use, once the flow has passed through the inlet, it reaches the flow sensing channel having a substantially flat surface. Since the surface of the flow sensing channel is substantially flat, the fluid flow through the flow sensing channel is parallel to the surface flow of the flow sensing channel and does not encounter interference or a reduced number of interferences such as corners of the flow sensor (flow sensing die) within the flow sensing channel. Therefore, the device of the present disclosure reduces turbulence through the sensor assembly, particularly turbulence around the flow sensing surface of the flow sensor, and improves the functionality of the flow sensor assembly.

[0027] Disturbances such as corners of the flow sensor may exist within the flow sensor but not outside the flow sensing channel and therefore do not increase turbulence in the flow sensing channel.

[0028] The planar surface of the flow sensing channel can be the first surface closest to the first substrate and defined by the flow sensor. The substantially planar surface can include the surface of the flow sensor and the area of ​​the flow sensing channel surface surrounding the flow surface. Thus, the surface of the flow sensor can be flush or level with the surface of the area surrounding the flow sensor.

[0029] Alternatively, the substantially flat surface may be the second surface farthest from the first substrate and defined by the cover.Both the first and second surfaces of the flow sensing channel may be substantially flat to reduce turbulence.

[0030] The flow sensor assembly may also include one or more extension members laterally adjacent the flow sensor.The extension members may be one or more separate components in physical contact with the flow sensor, or may be one or more extensions of the flow sensor itself.

[0031] A fluid flow sensor assembly may include the following elements: (i) a flow sensing die (or flow sensor) including a flow sensing surface including a flow sensing structure; (ii) a substrate; (iii) a cover; (iv) a flow inlet (or flow inlet channel); (v) a flow outlet (or flow outlet channel); (vi) a device for reducing turbulence near the flow sensing surface of the flow sensing die; and (vii) a flow channel for directing fluid from the flow inlet to the flow outlet. The flow channel is created by assembling elements (i) through (vi).

[0032] One or more of the flow inlet channel, the flow outlet channel, or the flow sensing channel may include one or more channel restrictors. A channel restrictor may be formed at any position within the flow channel. The term "channel restrictor" is used to refer to a restrictor positioned within a flow channel.

[0033] A flow sensing channel that directs fluid from the inlet to the outlet is created by assembling the lid on top of the substrate. The bottom surface (or first surface) of the flow sensing channel can be formed by an extension member (which can be a filler material) and the flow sensing surface of the flow sensing die. The bond wires can be perpendicular to the fluid flow and positioned in a manner that reduces their interaction with the fluid flow and, therefore, reduces the occurrence of undesirable turbulence.

[0034] The flow channel can have any cross-sectional geometry (e.g., square, rectangular, semicircular, irregular, etc.). The cross-sectional geometry can also vary along the length of the flow channel (e.g., the cross-section of the flow channel can be circular at the inlet and square at the flow sensing die portion of the flow sensing channel).

[0035] A specific case of a non-uniform flow channel cross-sectional area is the use of flow restrictors (i.e., the flow channel cross-sectional area is locally reduced). When integrated into a system using it, flow restrictors can be placed at the flow inlet and outlet to reduce the impact on the flow sensing performance of the flow sensor assembly. Flow restrictors can also be placed along the flow sensing channel near the flow sensing surface of the flow sensing die to locally increase the flow velocity and thereby improve flow sensing performance.

[0036] Another specific case of uneven flow channel cross-sectional area is the use of a reservoir or a gas collection chamber (i.e., the flow channel cross-sectional area is locally enlarged). The reservoir can also be placed at the inlet and outlet or along the flow sensing channel. By using a gas collection chamber, at the point where the inlet and / or outlet meets the flow sensing channel, there is an area in the inlet channel and / or outlet channel that has a much larger cross-sectional area than the rest of the inlet / outlet channel. The gas collection chamber can be placed at the inlet or outlet or both.

[0037] Furthermore, the flow sensing channel may run straight from the inlet to the outlet, may have a serpentine shape from the inlet to the outlet, or may have any other shape designed to improve the performance of the flow sensor assembly.

[0038] The extension member may include a filler material adjacent to the flow sensor and on the first substrate. The filler material or gel may extend across the remaining width of the flow sensing channel where the flow sensor is not present and may have a substantially flat top surface extending across the width of the flow sensing channel. The filler material may extend above the first substrate to substantially the same height as the flow sensor on the first substrate, such that the flow sensor and the filler material together form a flat surface (the first surface of the flow sensing channel) along the entire length of the flow sensing channel. In other words, the surface of the filler material may be flush with the surface of the flow sensor to form a single flat surface along the entire length of the flow sensing channel.

[0039] The flow sensor assembly may further comprise a rim to retain the filler material. The rim may be an integral part of the first substrate, the cover, or may be a separate component of the flow sensor assembly.

[0040] The substrate may include an edge; and the edge may be an integral part of the substrate. Alternatively, the edge may be an integral part of a cover or an additional component assembled to the substrate as part of the flow sensor assembly process. Thus, a cavity is formed between the edge and the flow sensing die. To reduce turbulence near the flow sensing surface of the flow sensing die, the cavity may be filled with a filler material. Depending on the filler deposition method, the surface topology of the filler may be concave or convex. Interestingly, the filler material may also protect the substrate bond pads and provide partial protection for the bond wires.

[0041] The shape of the rim can have sloped, vertical or backward sloping sidewalls as long as the cavity within the rim contains the flow sensing die.The rim can wrap around the package and can be done with any shape (e.g., circular, square, oval, square with rounded edges).

[0042] The filler material can be any material with suitable electrical, thermal, mechanical and chemical properties (e.g., a polymer, more specifically, a gel, resin, epoxy, ceramic, metal, semiconductor, or a combination thereof). The filler material is electrically insulating, thermally conductive, thermomechanically stable (i.e., does not immediately expand or contract and / or does not expand or contract when exposed to varying temperatures), and chemically stable (i.e., does not immediately absorb, adsorb, or desorb molecules). The filler material can be deposited (e.g., printed, syringe dispensed, sprayed, etc.) in a manner compatible with forming other elements of a flow sensing assembly with high reproducibility. A curing step can be used to change the phase of the filler from a liquid to a solid.

[0043] The filler material may be configured to not overlap the upper surface of the flow sensor.Due to surface tension, the filler material may have a concave or convex meniscus.

[0044] Alternatively, when the flow sensor is heated in use, the filler material may overlap slightly with the flow sensor. This may be achieved using a filler material having a concave or convex meniscus. Although the filler material may be configured to reduce overlap between the filler material and the flow sensor.

[0045] The flow sensor assembly may include bond wires electrically connected to the flow sensor, and the filler material may be configured to cover the bond wires. The filler material may completely encapsulate the bond wires; this reduces turbulence caused by the bond wires. Alternatively, the filler material may partially encapsulate the bond wires, and the bond wires may be configured to reduce interaction with fluid flowing through the fluid flow sensor assembly.

[0046] Due to surface tension effects, the filler material can completely encapsulate the bond wires and die bond pads for additional protection.

[0047] The extension member may include an extension portion of the flow sensor. The extension portion may be an integral part of the flow sensor. The extension portion may be a region of the substrate and dielectric layer, or may be another extension portion of a different type of flow sensor without a substrate and dielectric layer.

[0048] The cover may define one or more apertures, and the flow inlet channel may include a channel passing through one of the apertures. The flow inlet channel may be configured substantially perpendicular to the flow sensing channel, and the extension member may extend below the flow inlet channel. The extension member may extend along the entire width of the inlet channel. These features allow the fluid flow from the flow inlet channel to flow onto a substantially flat surface without interference upon reaching the flow sensing channel.

[0049] Alternatively or additionally, the outflow channel may comprise a channel through one of the apertures.The outflow channel may be configured substantially perpendicular to the flow sensing channel, and the extension member may extend below the outflow channel.

[0050] The top surface of the lid can be substantially flat, such that the inlet and outlet channels terminate on the top surface of the lid. The top surface can be defined as the outer surface of the lid extending in a lateral direction substantially parallel to the flow sensing channel. The apertures or openings defining the inlet and outlet channels can be flat.

[0051] Alternatively, the cover may include one or more protrusions on an outer surface of the cover, and the one or more holes may extend through the one or more protrusions. The protrusions may include hoses. The protrusions may extend away from the flow sensing channel.

[0052] The protrusion may be substantially perpendicular to the flow sensing channel, and the flow inlet channel and the flow outlet channel may be substantially perpendicular to the sensing channel.In this embodiment, fluid enters and leaves the flow sensor in opposite directions.

[0053] Alternatively, the protrusion may be substantially parallel to the sensing channel, and the flow inlet channel and the flow outlet channel may be substantially parallel to the sensing channel.In this embodiment, fluid enters and leaves the flow sensor in the same direction.

[0054] The flow sensor assembly may include a cover with a flow inlet and a flow outlet, each of which includes a flexible tube to facilitate mechanical connection to a system in which the flow sensor assembly is used. The flexible tube may have any geometry that facilitates mechanical connection to a system in which the flow sensor assembly is used. For example, the flexible tube may have barbs, grooves, protrusions, or a combination of these to enhance friction with the tubing or any other device connected to the flexible tube. The number, size, and location of the inlet and outlet within the flow sensor assembly may vary depending on the application requirements.

[0055] The first substrate and the cover can cooperate to define an inlet channel and an outlet channel. In other words, the inlet channel and the outlet channel can be defined by the cooperation of the shapes of the first substrate and the cover, and / or can be defined in the area between the first substrate and the cover on either side of the flow sensing channel.

[0056] The inlet and outlet channels can be defined on opposite surfaces of the flow sensor. In other words, the inlet and outlet channels can be on opposite sides of the flow sensor, allowing fluid to travel through the sensor in one direction. Fluid enters in the same direction as it exits, so the sensor can be used with continuous flow.

[0057] The cover may further include a cover flow restrictor, and the extension member may extend below the entire length of the cover flow restrictor. The term "cover flow restrictor" is used to refer to a flow restrictor formed on the cover. The cover flow restrictor may be positioned on a lower surface of the cover. The lower surface of the cover may be defined as a surface of the cover that defines the flow sensing channel and is internal to the flow sensor assembly.

[0058] The cover can include a flow restrictor positioned along the flow path near the flow sensing surface of the flow sensing die to locally increase the flow velocity and thereby improve flow sensing performance. This can be used in applications where the flow sensor assembly is soldered to a surface over which a fluid flows and the application requires measuring a characteristic of the flowing fluid. This can be used in embodiments with a rim and filler material, or in embodiments where the extension member is an extension of the flow sensor.

[0059] The flow sensor assembly may further include an integrated circuit or circuit positioned between the flow sensor and the first substrate. In other words, the first substrate, the integrated circuit, and the flow sensor may be stacked in the order of the first substrate, the integrated circuit, and the flow sensor. In embodiments having a filler material, the filler material may encapsulate the integrated circuit.

[0060] The flow sensor assembly may also include an integrated circuit or circuit positioned laterally spaced apart from the flow sensor and on the first substrate, wherein the one or more extension members cover the integrated circuit. In other words, the flow sensor and the integrated circuit may be positioned side by side on the first substrate. The extension member may completely cover the integrated circuit. In embodiments having a filler material, the filler material may encapsulate the integrated circuit.

[0061] The flow sensor assembly may also include an integrated circuit (IC) die. The flow sensing die can be stacked on top of the IC die to reduce the form factor of the overall flow sensor assembly. Alternatively, the flow sensing die and the IC die can be assembled side by side. In both cases, the filler material can provide protection for the IC die. The flow sensing die can be directly connected to the IC die via bonding wires, or indirectly connected to the IC die via electrical connections through the substrate. The flow sensing die can have through silicon vias (TSVs) to avoid the presence of bonding wires and even further reduce the occurrence of unwanted turbulence. Advantageously, flow sensors with TSVs can be facilitated by 3D stacking technology, whereby the flow sensing die is located on top of an IC (e.g., an ASIC), thereby reducing the size of the sensor system.

[0062] Alternatively or additionally, the circuit blocks can be integrated into the flow sensor itself. The thin film of the flow sensor can occupy a small area of ​​the flow sensing surface, leaving a large area for monolithic integration of the circuit blocks within the flow sensing die. The circuits can include IPTATs, VPTATs, amplifiers, analog-to-digital converters, digital-to-analog converters, memories, RF communication circuits, timing blocks, filters, or any other devices for driving, readout, and electrical signal processing, as well as communicating with the outside world. For example, in the case of a thermal flow sensor, a heating element driven in a constant temperature mode would result in enhanced performance, and having an on-chip device implementing this driving method would result in a significant advancement over prior art flow sensors. Furthermore, the known 3ω driving method can be implemented via an on-chip device or any other driving method required to achieve specific performance (e.g., power consumption, sensitivity, dynamic response, range, fluid property detection, etc.).

[0063] A flow sensor may include: a sensor substrate, a dielectric layer, and a sensing element, wherein the sensor substrate includes an etched portion; the dielectric layer is positioned on the sensor substrate, wherein the dielectric layer may include at least one dielectric film positioned above the etched portion of the sensor substrate; and the sensing element is positioned on or within the dielectric film.

[0064] The sensing element may include a metal layer positioned within a dielectric film. The metal layer may include a heater, a temperature sensor, or other types of sensing elements used in flow sensors.

[0065] A flow sensing die or flow sensor may include: a substrate including an etched portion; a dielectric region positioned on the substrate, wherein the dielectric region includes a dielectric film on the region of the etched portion of the substrate; and means for sensing one or more properties of a fluid (e.g., velocity, flow velocity, applied wall shear stress, absolute pressure, differential pressure, temperature, direction, thermal conductivity, diffusion coefficient, density, specific heat, kinematic viscosity, etc.). The flow sensing die may be a thermal flow sensor, and the means for sensing one or more properties of the fluid may include a heating element and a temperature sensor. The flow sensing die may be a mechanical flow sensor, and the means for sensing one or more properties of the fluid may include a piezoelectric element.

[0066] The starting substrate can be silicon or silicon on insulator (SOI). However, any other substrate that combines silicon with another semiconductor material compatible with existing CMOS manufacturing processes can be used. The use of CMOS manufacturing processes ensures the manufacturability of sensors in large quantities, at low cost, with high reproducibility and wide availability in factories that support this process. CMOS processes can also be used for on-chip circuits that enhance sensor performance and facilitate system integration.

[0067] One or more thin films can be formed by back-etching using deep reactive ion etching (DRIE) of the substrate, which produces vertical sidewalls and can therefore reduce the size and cost of the sensor. However, back-etching can also be accomplished using an anisotropic etch such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide), which produces sloped sidewalls. Thin films can also be formed by front-side etching or a combination of front-side and back-side etching to produce suspended thin film structures supported by only two or more beams. The thin films can be circular, rectangular, or rectangular with rounded corners to reduce stress in the corners, but other shapes are also possible.

[0068] The dielectric film may include silicon dioxide and / or silicon nitride. The film may also include one or more layers spin-coated on glass, and a passivation layer over one or more dielectric layers. The use of materials with low thermal conductivity (e.g., dielectrics) can significantly reduce power consumption and increase the temperature gradient within the film, which has direct benefits in terms of sensor performance (e.g., sensitivity, frequency response, range, etc.).

[0069] The membrane may also have other structures made of polysilicon, single crystal silicon or metal. These structures may be embedded within the membrane or may be embedded above or below the membrane. More generally, these structures may also be outside the membrane and / or bridge between the inside and outside of the membrane. The main purposes of the structures are: (i) to design the thermomechanical properties of the membrane (e.g. stiffness, temperature profile, etc.); (ii) to design the fluid dynamics interaction between the fluid and the membrane; (iii) to protect the membrane from unwanted surface penetration of the filler material. The structures may have any geometry, be made of any material suitable for purposes (i) to (iii), and be implemented as part of the die manufacturing process or as part of the flow sensor assembly process.

[0070] The dielectric region can include a dielectric layer or multiple layers including at least one dielectric layer. Generally speaking, the dielectric film region can be located immediately adjacent to the etched portion of the substrate. The dielectric film region corresponds to the area of ​​the dielectric region above (or below, depending on the configuration) the etched cavity portion of the substrate. For example, in a flip-chip configuration, the dielectric film will be shown below the etched cavity portion of the substrate. Each dielectric film region can be above a single etched portion of the semiconductor substrate.

[0071] The flow sensor may include a passivation layer positioned on the dielectric layer.

[0072] The top surface of the passivation layer can be configured as non-planar. The top surface of the passivation layer can be defined as the surface adjacent to the flow sensing channel or flow sensing surface. The top surface of the passivation layer can include a protrusion extending away from the dielectric layer. The protrusion can include a wall or ridge. A stack can be used within the dielectric layer to support the wall or ridge.

[0073] A wall may be present on the flow sensing surface of the flow sensing die. In the event that filler material penetrates onto the flow sensing surface of the flow sensing die, the wall acts as a barrier to the filler material, thereby preventing the filler material from interacting with the flow sensing structure of the flow sensing surface of the flow sensing die. The wall may be a byproduct of a non-planar manufacturing process. For example, a metal structure within a metal layer may be implemented such that the flow sensing surface with the extrusion follows the pattern of the metal structure within the metal layer. This effect may be further enhanced if the metal structures are implemented on top of each other in different metal layers.

[0074] The top surface of the passivation layer may include one or more recesses. The recesses, grooves, or notches may be etched portions of the passivation layer. These allow excess fill material to expand or penetrate into the recesses, for example when the sensor assembly is heated during use. This reduces penetration of the fill material into the membrane.

[0075] A groove or recess may be present on the flow sensing surface of the flow sensing die. In the event that filler material penetrates onto the flow sensing surface of the flow sensing die, the groove serves as a reservoir for the filler material. This prevents the filler material from interacting with the flow sensing structures on the flow sensing surface of the flow sensing die.

[0076] The protrusions of the passivation layer can be used as an alternative to or in addition to the grooves in the passivation layer. This reduces the penetration of the filler material into the dielectric film, which would degrade the functionality of the flow sensor.

[0077] The dielectric film may define a through hole. The through hole or hole may extend through the film to allow fluid to flow through the flow sensor.

[0078] To facilitate the assembly process and reduce failures during soldering of the flow sensor assembly, the membrane may include through holes (or membrane cavity vents). The vents reduce any pressure buildup within the membrane cavity that could cause rupture, damage, or stress to the membrane.

[0079] The first substrate may define a hole. The hole of the first substrate and the through hole of the dielectric film may form a hole through the flow sensor assembly.

[0080] The first substrate may have vents or holes. The vents reduce any pressure buildup in the cavity below the membrane, thereby reducing the risk of failure during packaging the flow sensing die onto the substrate and soldering the flow sensor assembly to a second substrate (e.g., a PCB).

[0081] One or more of the flow inlet channel, the flow outlet channel, and the flow sensing channel may include a protective layer. The protective layer may be a protective coating. The protective coating may be applied to all flow channels, or only to the top surface of the extension member forming the flow sensing channel, or may be formed over the entire flow sensor assembly. In embodiments where the first substrate has a hole, the hole may be coated with the protective coating.

[0082] The flow sensor assembly may further include bonding pads positioned on the outer surface of the flow sensor assembly. The first substrate may include additional bonding pads, referred to as internal bonding pads. The flow sensor may include additional bonding pads, referred to as die bonding pads. The outer surface of the flow sensor assembly may be plastic, and the (outer) bonding pads may be made of metal. The outer bonding pads may form an electrical connection between the outer surface of the assembly and the inner bonding pads of the lead frame (first substrate). The inner bonding pads may form an electrical connection with the die bonding pads via bonding wires. In an embodiment with a protective coating, the bonding pads may be exposed and not covered by the protective coating.

[0083] The flow channel walls may be partially or completely covered and protected by a protective layer. The protective layer may be a conformal layer, thereby conforming to the topology of the flow channel walls. Bond lines may also be conformally coated with the protective layer. Any other components within the flow channel that would otherwise come into contact with the fluid flow may also be conformally coated with the protective layer.

[0084] The entire flow sensor assembly (not just the flow channel walls) can be coated with a conformal protective layer.

[0085] Alternatively, the protection layer can be deposited at the wafer level. In this case, only the flow sensing die will be protected by the protection layer.

[0086] The protective layer may also be deposited during the assembly process or at the end of the assembly. In these cases, only a portion of the flow sensor assembly or the entire flow sensor assembly will be protected by the protective layer.

[0087] The protective layer can protect the fragile elements of the flow sensor assembly from the influence of aggressive media (such as aggressive liquids, corrosive gases, etc.), and can also improve the biocompatibility of the flow sensor assembly, for example in medical applications, and generally avoid direct interaction between some or all elements of the flow sensor assembly and the fluid to be measured and / or the environment.

[0088] According to another aspect of the present disclosure, a method of manufacturing a flow sensor assembly is provided, the method comprising: forming a first substrate; forming a flow sensor on the first substrate; forming a cover over the flow sensor; forming a flow inlet channel; forming a flow outlet channel, wherein a surface of the flow sensor and a surface of the cover cooperate to form a flow sensing channel between the flow inlet channel and the flow outlet channel; and wherein the surface of the flow sensing channel is substantially flat over the entire length of the flow sensing channel.

[0089] A method of manufacturing a flow sensor assembly may include forming a substrate, forming a lid, assembling a flow sensing die on the substrate in a manner that minimizes turbulence near a flow sensing surface of the flow sensing die, and assembling the lid.

[0090] The flow sensor assembly may further include one or more guide structures, wherein the guide structures may at least partially separate the flow sensing channel from one or more regions between the inlet channel and the outlet channel external to the flow sensing channel or additional flow channels.

[0091] According to another aspect of the present disclosure, a flow sensor assembly is provided, comprising: a first substrate; a flow sensor positioned on the first substrate; a cover positioned above the sensor; a flow channel inlet; a flow channel outlet; and one or more guide structures, wherein the guide structures at least partially separate the flow sensing channel from one or more regions between the inlet channel and the outlet channel outside the flow sensing channel, and wherein a surface of the flow sensor, a surface of the cover, and a surface of the one or more guide structures cooperate to form a flow sensing channel between the flow inlet channel and the flow outlet channel.

[0092] The guiding structure may be designed to separate the flow channel into one or more additional flow channels, with a main channel (flow sensing channel) over the center of the flow sensor and one or more side channels surrounding the flow sensor.

[0093] The one or more guide structures may comprise one or more protrusions on the inner surface of the cover. The guide structure may be incorporated into or formed on the top of the flow channel, the top being provided by the cover. When incorporated into the cover, the guide structure may or may not extend downwardly and contact the surface of the flow sensing die, thereby forming a sealed channel.

[0094] The one or more guide structures may include one or more protrusions on the surface of the flow sensor. The one or more guides may be formed on an extension member that is laterally adjacent to the flow sensor. The guide structure may be incorporated into the bottom surface of the bottom of the flow channel, the bottom surface being provided by the flow sensing die or the extension member. The guide structure may be included on the die or the extension member by micromachining methods (for example using SU8 material), or by post-processing by bonding an additional patterned substrate. When the guide structures are incorporated into the flow sensing die, they may or may not extend until they contact the lid, thereby forming a sealed channel.

[0095] The one or more guiding structures may completely separate or isolate the flow sensing channel from one or more regions between the inlet and outlet channels or additional flow channels outside the flow sensing channel.The guiding structures may provide a flow restrictor in the flow channel.

[0096] The flow sensor assembly may include a bond wire electrically connected to the flow sensor, and the guide structure may separate the bond wire from the flow sensing channel.The bond wire may be positioned in one or more areas between the inlet channel and the outlet channel outside the flow sensing channel.

[0097] The flow channel may include one or more guide structures, which may be located on the cover or the flow sensing die. The guide structures help isolate eddy currents from the flow sensing surface within the flow sensing channel, thereby reducing the amount of interference experienced by the flow sensor. Thus, the apparatus of the present disclosure reduces turbulence through the sensor assembly, thereby improving the linearity and sensitivity of the flow sensor assembly.

[0098] The flow sensing channel that guides the fluid from the inlet to the outlet is created by the assembly of the cover and the guide structure on top of the substrate. The bond wires can also be outside the guide structure and outside the flow sensing channel to further reduce their interaction with the fluid flow.

[0099] The guide structure may have any cross-sectional geometry (eg square, rectangular, chamfered edges) and may extend from the inlet flow channel to the outlet flow channel.

[0100] The guide structure may have a non-uniform height along the flow channel.

[0101] The guide structure may have a lower height in areas closer to the inlet and outlet channels. The guide structure may have a greater height toward the center of the flow sensor assembly and closer to the flow sensor. In other words, the guide structure may extend further from the cover to the substrate in the center of the flow sensor assembly or further into the depth of the sensor assembly than below the inlet and outlet channels.

[0102] This uneven height (particularly the lower height closer to the flow inlet and flow outlet channels) causes the vortex generated by the inlet to be able to enter the side (additional flow) channels separated from the main flow induction channel or channels.

[0103] The guide structure can have a greater height around the flow channel inlet. In other words, the guide structure can extend from the cover further into the substrate or extend further in the depth of the sensor assembly below the inlet and outlet channels than in the center of the flow sensor assembly. When formed in conjunction with the filler material, this means that the side channels are inaccessible, thereby forcing all fluid to flow through the flow sensing die and improving the sensitivity and performance of the flow sensor. The flow channel bottom surface is formed by the flow sensing die in conjunction with the filler material, the flow channel top is formed by the cover, and the flow channel sidewalls are formed by the guide structure. The cross-sectional area of ​​the flow channel has been reduced to increase the velocity of flow through the flow sensor. The side channels exist but are inaccessible to the fluid flow, and any bond wires in this area are protected from any corrosive substances in the fluid flow.

[0104] The lid may also include a lip or other protrusion on its outer surface. The lip can increase the size of the lid. The purpose of this protrusion is to provide an increased platform area for better connection and to provide the ability to identify component orientation and pin markings. Such a protrusion can be any desired shape, for example, to make all four lid "shoulders" available for easier connection and alignment.

[0105] The flow sensor assembly may further include a gasket, wherein the outer surface of the cover abuts (directly contacts) the gasket.The gasket may be positioned on the exterior of the flow sensor cover around the flow inlet channel and the flow outlet channel.

[0106] The gasket may be designed so that it forms a seal around and between the ports to ensure that, in addition to flow not short-circuiting between the inlet and outlet channels, there is no leakage outside the component fixture.

[0107] Any material can be used to create a rubber gasket that provides suitable sealing performance within the required operating range, for example, rubber (silicone, EPDM, butyl rubber, and SBR) or foam (EPDM, neoprene, polyethylene, polyurethane, and vinyl nitride).

[0108] Gaskets can be cut to any shape best suited to create an airtight seal. This includes varying thickness for correct pressure and temperature, as well as external and internal cuts to suit port sizes and connections to external fixtures.

[0109] In the specific case of small foam gaskets, a PET reinforcement film may be used in the center of the gasket to aid in the precise cutting of the gasket shape.

[0110] The flow sensor assembly may also include an adhesive or adhesive tape between the gasket and the cover. The gasket may be adhered to the flow sensor cover or to a fixture placed therein using a pressure-sensitive adhesive (PSA). The tape may be made of any material best suited for the application, including solid rubber and foam rubber, and may or may not include a reinforcing film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0112] Figure 1A A first flow sensor assembly according to the prior art is shown;

[0113] Figure 1B A second flow sensor assembly according to the prior art is shown;

[0114] Figure 1C A third flow sensor assembly according to the prior art is shown;

[0115] Figure 1D A fourth flow sensor assembly according to the prior art is shown;

[0116] Figure 2 shows a schematic top view of a flow sensor assembly;

[0117] Figure 3A Shown along Figure 2 A schematic cross section of a flow sensor assembly with a filling material taken along the AA' cutting line;

[0118] Figure 3B Shown along Figure 2 A schematic cross section of the flow sensor assembly with the filling material taken along the BB' cutting line;

[0119] Figure 4 shows a schematic cross-section of a flow sensor assembly with fill material having an inlet and outlet including a flow restrictor and a flow sensing die stacked on top of an ASIC;

[0120] Figure 5 shows a schematic cross-section of a flow sensor assembly with fill material having a flow sensing die arranged side-by-side with an ASIC;

[0121] Figure 6 shows a schematic cross-section of a flow sensor assembly having an inlet and an outlet at the top of a flow sensing die;

[0122] Figure 7 shows a schematic cross section of a flow sensor assembly with a filler material having an inlet and an outlet arranged parallel to a flow channel with a flow restrictor;

[0123] Figure 8 shows a schematic cross-section of a flow sensor assembly having an inlet and an outlet arranged parallel to a flow channel with a flow restrictor;

[0124] Figure 9 shows a schematic cross-section of a flow sensor assembly with filler material protecting the bond wires;

[0125] Figure 10 shows a schematic cross section of a flow sensing die with grooves on the surface of the flow sensing die;

[0126] Figure 11 shows a schematic cross section of a flow sensing die with a wall on the surface of the flow sensing die;

[0127] Figure 12 shows a schematic top view of a flow sensing die having structures (grooves or walls) on the surface of the flow sensing die to protect the membrane from unwanted surface penetration of the fill material;

[0128] Figure 13 shows a schematic cross-section of a flow sensor assembly having an inlet and outlet on top of a flow sensing die and a hole in the substrate below a thin film cavity;

[0129] Figure 14 shows a schematic cross section of a flow sensor assembly with a filling material having an inlet and an outlet arranged parallel to a flow channel with a flow restrictor and having a protective layer on the walls of the flow channel;

[0130] Figure 15 shows a schematic cross-section of a flow sensor assembly having an inlet and an outlet on top of a flow sensing surface coated with a protective layer, and a hole in the substrate below the thin film cavity;

[0131] Figure 16 shows a schematic cross-section of a flow sensor assembly coated with a protective layer, wherein only the solder pads are exposed;

[0132] Figure 17 A schematic top view of a flow sensor assembly is shown, wherein the flow sensor assembly has a guide structure.

[0133] Figure 18a Shown is a section taken through cutting line BB Figure 17 A schematic cross-section of a flow sensor assembly;

[0134] Figure 18b Shown is a cut through the cutting line AA Figure 17 A schematic cross-section of a flow sensor assembly;

[0135] Figure 18c and 18d shows a comparison of computational fluid dynamics (CFD) simulations of a flow sensor assembly without and with a guide structure;

[0136] Figure 19a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein the guide structure has a varying height;

[0137] Figure 19b Shown Figure 19a 3D diagram of the lid interior design of an example.

[0138] Figure 20a and 20b shows a schematic cross-section of a flow sensor assembly wherein a filler material is applied to create a flat surface;

[0139] Figure 21ashows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein the cover includes a reservoir or plenum into which the flow may be dispersed;

[0140] Figure 21b Shown Figure 21a 3D diagram of the interior design of the lid of an embodiment;

[0141] Figure 22a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein guides near the inlet and outlet are higher than the center of the subassembly above the flow sensing die;

[0142] Figure 22b Shown Figure 22a 3D diagram of the interior design of the lid of an embodiment;

[0143] Figure 22c Shown according to Figure 22a A schematic cross section taken along the CC cutting line shown in FIG;

[0144] Figure 23a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein there is no filler material in the cavity between the flow sensing die and the edge of the substrate, thereby providing a fluid path around the bottom of the substrate for separating eddy flow from the main channel;

[0145] Figure 23b Shown Figure 23a 3D diagram of the interior design of the lid of an embodiment;

[0146] Figure 24a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein a guide structure is formed on a flow sensing die;

[0147] Figure 24b Shown Figure 24a 3D diagram of the interior design of the lid of an embodiment;

[0148] Figure 25a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein the cover has a platform structure;

[0149] Figure 25b Shown Figure 25a 3D diagram of the interior design of the lid of an embodiment;

[0150] Figure 26a shows a schematic cross-section of a flow sensor assembly having a platform structure formed on a flow sensing die according to an embodiment of the present disclosure;

[0151] Figure 26b Shown Figure 26a3D graph of the cross section;

[0152] Figure 27a and 27b shows a schematic cross-section of a flow sensor assembly in which a flow sensing element is contained within a flow sensing channel and a temperature sensing element is positioned in a side channel, including a flow control guide;

[0153] Figure 28a shows a schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure, wherein a guide structure contacts a flow sensing surface;

[0154] Figure 28b Shown Figure 28a 3D diagram of the interior design of the lid of an embodiment;

[0155] Figure 29 shows a 3D diagram of a flow sensor assembly according to an embodiment of the present disclosure, wherein the sensor assembly has a gasket; and

[0156] Figure 30 A 3D diagram of a flow sensor assembly with a gasket and adhesive tape is shown according to an embodiment of the present disclosure. Specific embodiments

[0157] Some examples of the disclosed apparatus are given in the accompanying drawings.

[0158] Figure 2 A schematic top view of a flow sensor assembly according to an embodiment of the present disclosure is shown, comprising a flow sensing die or flow sensor 1, comprising a flow sensing surface 2, which comprises a thin film 3. The flow sensing die 1 is electrically connected to a substrate (first substrate) via bonding wires 4. The substrate comprises an edge (backing ring) 5. The flow sensor assembly further comprises a cover 6, which comprises an inlet or flow inlet channel 7 and an outlet or flow outlet channel 8, both of which comprise a flexible tube 9.

[0159] Figure 3A Shown Figure 2 Schematic cross-section of a flow sensor assembly taken along cutting line AA', comprising a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. Flow sensing die 1 is electrically connected to substrate 10 via bonding wires 4. Substrate 10 includes an edge 5. The gap between edge 5 and flow sensing die 1 is filled with a filling material 11 having a convex surface topology. The flow sensor assembly also includes a cover 6.

[0160] For connection purposes, the flow sensor assembly has external bond pads positioned on the outer surface of the flow sensor assembly. Substrate 10 also has bond pads, referred to as internal bond pads, and the flow sensor may include additional bond pads on the dielectric film, referred to as die bond pads. The external bond pads form an electrical connection between the outer surface of the assembly and the internal bond pads of the substrate. The internal bond pads form an electrical connection to the die bond pads via bond wires.

[0161] Figure 3B Shown Figure 2 A schematic cross-section of a flow sensor assembly taken along cutting line BB' includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. A substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filling material 11 having a concave or convex surface topology. The flow sensor assembly also includes a cover 6, which includes an inlet 7 and an outlet 8, both of which include a flexible tube 9.

[0162] exist Figure 2 、 Figure 3A and Figure 3B In the example shown in , the flow sensing die is assembled onto a substrate (e.g., a lead frame, a printed circuit board, or any other substrate that mechanically supports the die and provides electrical connections from the die to the outside world). The substrate includes an edge. The edge can be an integral part of the substrate, an integral part of the cover, or an additional element assembled to the substrate as part of the flow sensor assembly process. Thus, a cavity is formed between the edge and the flow sensing die. In order to reduce turbulence near the flow sensing surface of the flow sensing die, the cavity is filled with a filler material. The surface topology of the filler can be concave or convex depending on the filler deposition method. The filler material can also protect the substrate bonding pads and provide partial protection for the bonding wires.

[0163] The flow sensor assembly also has a cover with a flow inlet and a flow outlet, both of which include flexible tubes to facilitate mechanical connection to the system in which it is used. The flexible tubes can have any geometry that facilitates mechanical connection to the system in which the flow sensor assembly is used. For example, the flexible tube can have barbs, grooves, protrusions, or a combination of these to enhance friction with the tubing or any other device connected to the flexible tube. The number, size, and location of the inlet and outlet in the flow sensor assembly can vary depending on the application requirements.

[0164] Figure 4A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein both the inlet and outlet have flow restrictors and the flow sensing die is stacked on top of an ASIC. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. The flow sensing die 1 is stacked on top of an IC 12. A substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filler material 11 having a concave surface topology. The flow sensor assembly also includes a cover 6, which includes an inlet 7 and an outlet 8, both of which include a hose 9 and a channel flow restrictor 13.

[0165] The non-uniform flow channel cross-sectional area is achieved by using flow restrictors (ie, the flow channel cross-sectional area is locally reduced). The flow restrictors are placed at the flow inlet and outlet to reduce the impact on the flow sensing performance of the flow sensor assembly when integrated into a system using it.

[0166] The protrusion or hose is substantially perpendicular to the flow sensing channel, and the flow inlet channel and the flow outlet channel may then be substantially perpendicular to the sensing channel.In this embodiment, fluid enters and leaves the flow sensor in opposite directions.

[0167] The flow sensing die is stacked on top of the IC die to reduce the overall form factor of the flow sensor assembly. Alternatively, the flow sensing die and the IC die can be assembled side by side, as shown in Figure 3. In both cases, the filler material provides protection for the IC die.

[0168] Figure 5 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein a flow sensing die is positioned laterally adjacent to an ASIC. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. The flow sensing die 1 is assembled side-by-side with an IC 12. The flow sensing die 1 is electrically connected to the IC 12 via bonding wires 4. The IC is electrically connected to a substrate 10. The substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filler material 11 that completely covers the IC 12. The flow sensor assembly also includes a lid 6.

[0169] Figure 6A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein both the inlet and outlet terminate at the top surface of a lid. Both the inlet 7 and outlet 8 are positioned above the flow sensor 1, which has integral extensions to reduce turbulence. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a membrane 3. The flow sensor assembly also includes a lid 6, which includes an inlet 7 and an outlet 8. The flow sensing die 1 includes a flow sensing surface 2 that extends below the inlet 7 and outlet 8.

[0170] In Figures 3 to Figure 6 In the embodiment, the surface within or surrounding the flow sensor may have a first region below the channel inlet 7 and a second region below the channel outlet 8, and the surface between the first region and the second region is substantially flat.

[0171] Figure 7 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the inlet and outlet are arranged parallel to the flow sensing channel and the device has a lid flow restrictor. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. A substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filler material 11. The flow sensor assembly also includes a lid 6, which includes an inlet 7, an outlet 8, and a lid flow restrictor 13.

[0172] In this embodiment, a flow sensor assembly includes a flow sensing die, the flow sensing die including a flow sensing surface, and the flow sensing surface including a thin film. The flow sensor assembly also includes a lid and a substrate having an edge. The flow sensing die is assembled on the substrate. Thus, a cavity is formed between the edge and the flow sensing die. To reduce turbulence near the flow sensing surface of the flow sensing die, the cavity is filled with a filler material. The lid is assembled onto the edge of the substrate.

[0173] The cover includes a flow restrictor positioned along the flow path near the flow sensing surface of the flow sensing die to locally increase flow velocity and thereby improve flow sensing performance. When the cover is assembled onto the edge of the substrate, a flow inlet, a flow outlet, and a flow path are created. The flow sensor assembly described in this embodiment is suitable for applications where the flow sensor assembly is soldered to a surface through which fluid is flowing and where it is necessary to measure characteristics of the flowing fluid.

[0174] Figure 8A schematic cross-section of a flow sensor assembly according to an embodiment of the present invention is shown, wherein the inlet and outlet are arranged parallel to the flow channel, the device has a lid flow restrictor, and the flow sensor has an extension. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a membrane 3. The flow sensor assembly also includes a substrate 10, a lid 6, which includes an inlet 7 and an outlet 8, and a flow restrictor 13.

[0175] In this embodiment, a flow sensor assembly includes a flow sensing die, the flow sensing die including a flow sensing surface, the flow sensing surface including a thin film. The flow sensor assembly also includes a cover and a substrate. The flow sensing die and the cover are assembled on the substrate. The cover includes a flow restrictor placed near the flow sensing surface of the flow sensing die along the flow channel to locally increase the flow velocity and thereby improve the flow sensing performance by reducing turbulence near the thin film on the flow sensing surface of the flow sensing die. When the cover is assembled on the edge of the substrate, a flow inlet, a flow outlet, and a flow channel are generated. The flow sensor assembly described in this embodiment is suitable for applications where the flow sensor assembly is welded to a surface where a fluid is flowing, and the application requires measuring the characteristics of the flowing fluid.

[0176] exist Figure 7 and Figure 8 In FIG, the flow channel surface surrounding the flow sensor and the flow channel surface in the entire area below the flow restrictor 13 are substantially flat. Both ends of the flow restrictor 13 serve as guides for fluid to enter the flow channel, and the same is true for the input and output points of the flow channel, and the surfaces below them are substantially flat.

[0177] Figure 9 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein a filler material encapsulates and protects the bond wires. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. The flow sensing die 1 is electrically connected to a substrate 10 via bond wires 4. The substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filler material 11 that covers the bond wires 4. The flow sensor assembly also includes a lid 6.

[0178] In this embodiment, a flow sensor assembly includes a flow sensing die, the flow sensing die including a flow sensing surface, the flow sensing surface including a thin film. The flow sensor assembly also includes a lid and a substrate with an edge. The flow sensing die is assembled on the substrate. As a result, a cavity is formed between the edge and the flow sensing die. To reduce turbulence near the flow sensing surface of the flow sensing die, the cavity is filled with a filler material. Due to surface tension effects, the filler material completely encapsulates the bonding wires and die bonding pads for additional protection. The lid is assembled on the edge of the substrate.

[0179] Figure 10 A schematic cross-section of a flow sensing die 1 that can be used in a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the flow sensor 1 has grooves on the surface of the flow sensing die. The flow sensor 1 includes a flow sensing surface 2, which includes a thin film 3. The flow sensing die 1 also includes a passivation layer 14, a metal layer 15 that serves as a sensing element embedded in a dielectric layer 16, and a die substrate 17 that is partially etched through to obtain the thin film 3. The passivation layer 14 is also partially etched to obtain grooves 18 on the flow sensing surface 2. The thin film also includes a through hole 19.

[0180] In this embodiment, a groove is present on the flow sensing surface of the flow sensing die. In the event that filler material infiltrates onto the flow sensing surface of the flow sensing die, the groove serves as a reservoir for the filler material. This prevents the filler material from interacting with the flow sensing structures on the flow sensing surface of the flow sensing die.

[0181] Figure 11 A schematic cross-section of a flow sensing die 1 that can be used in a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the flow sensor 1 has walls on the surface of the flow sensing die. The flow sensor 1 includes a flow sensing surface 2, which includes a thin film 3. The flow sensing die 1 also includes a passivation layer 14, a metal layer 15 embedded in a dielectric layer 16, and a die substrate 17 that is partially etched through to obtain the thin film 3. The passivation layer 14 is also made non-planar by means of a metal stack 20 to obtain walls 21 on the flow sensing surface 2.

[0182] In this embodiment, a wall appears on the flow sensing surface of the flow sensing die. In the event that filler material penetrates onto the flow sensing surface of the flow sensing die, the wall acts as a barrier to the filler material, thereby preventing the filler material from interacting with the flow sensing structures on the flow sensing surface of the flow sensing die. The wall can be a byproduct of a non-planar manufacturing process. For example, metal structures within a metal layer can be formed, resulting in the flow sensing surface having an extrusion that follows the pattern of the metal structures within the metal layer. This effect can be further enhanced if the metal structures are formed on top of each other within different metal layers.

[0183] Figure 12A schematic top view of a flow sensing die 1 that can be used in a flow sensor assembly according to an embodiment of the present invention is shown, wherein the flow sensor 1 has structures (grooves or walls) on the surface of the flow sensing die for protecting the membrane from unwanted surface penetration of the filler material. The flow sensor 1 includes a flow sensing surface 2, which includes a membrane 3. A wire heater 22 is embedded in the membrane 3 and has a track 23 connected to a pad (not shown for simplicity). The membrane also includes a through hole 19. The flow sensing die 1 also includes structures 24 (made of grooves, walls, or a combination thereof) to prevent the filler material from penetrating the membrane 3.

[0184] Figure 13 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the inlet and outlet are on top of the flow sensing die and the flow sensor assembly has an aperture in the substrate below the membrane cavity. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a membrane 3. The flow sensor assembly also includes a lid 6, which includes an inlet 7 and an outlet 8. The flow sensing die 1 includes the flow sensing surface 2 extending below the inlet 7 and outlet 8. The substrate 10 includes an aperture 25.

[0185] In this embodiment, the substrate has vents. The vents reduce the pressure buildup in the cavity below the membrane, thereby reducing the risk of failure during packaging the flow sensing die onto the substrate and during soldering the flow sensor assembly onto a second substrate (e.g., a PCB).

[0186] Figure 14 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the flow sensor assembly has a protective layer on the walls of the flow channel. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. A substrate 10 includes an edge 5. The gap between the edge 5 and the flow sensing die 1 is filled with a filler material 11. The flow sensor assembly also includes a lid 6, which includes an inlet 7 and an outlet 8, and a flow restrictor 13. The flow channel created by the assembly of the lid 6 with the flow restrictor 13, the substrate edge 5, the filler material 11, and the flow sensing surface 2 is protected by a protective layer 26.

[0187] The flow channel walls are partially or completely covered and protected by the protective layer. The protective layer is a conformal layer and therefore follows the topology of the flow channel walls. The bonding wires can also be conformally coated with the protective layer. Any other components within the flow channel that would come into contact with the fluid flow without the protective layer can also be conformally coated with the protective layer.

[0188] The protective layer of this embodiment and Figure 15 and 16The protective layer of the illustrated embodiment protects fragile components of the flow sensor assembly from aggressive media, such as aggressive liquids, corrosive gases, etc. The protective layer also improves the biocompatibility of the flow sensor assembly, for example, in medical applications, and generally reduces direct interaction of some or all components forming the flow sensor assembly with the measured fluid and / or the environment.

[0189] Figure 15 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the flow sensor assembly has a flow sensing surface coated with a protective layer. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2 with a protective layer 26, wherein the flow sensing surface 2 includes a thin film 3. The flow sensor assembly also includes a cover 6, which includes an inlet 7 and an outlet 8. The flow sensing die 1 includes a flow sensing surface 2 extending below the inlet 7 and the outlet 8. The substrate 10 includes a hole 25. In this embodiment, the protective layer can be deposited at the wafer level. In this case, only the flow sensing die is protected by the protective layer.

[0190] Figure 16 A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the entire flow sensor assembly is coated with a protective layer, with only the solder outer bond pads being exposed. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a thin film 3. The flow sensor assembly also includes a cover 6, which includes an inlet 7 and an outlet 8. The flow sensing die 1 includes a flow sensing surface 2 extending below the inlet 7 and outlet 8. The substrate 10 includes a hole 25. The flow sensor assembly also includes a protective layer 26, which coats the entire assembly and exposes only the pads 27. In this embodiment, the entire flow sensor assembly (not just the flow channel walls) can be coated with a conformal protective layer.

[0191] Figure 17 A schematic top view of a flow sensor assembly according to an embodiment of the present disclosure is shown. The flow sensor assembly has a flow sensing die or flow sensor 1 having a flow sensing surface 2 and a thin film 3. The flow sensing die 1 is electrically connected to a substrate via bond wires 4. The substrate has an edge 5. The flow sensor assembly also has a lid 6 having an inlet channel 7 and an outlet channel 8.

[0192] Figure 18a Shown Figure 17 Schematic cross section of the flow sensor assembly taken along the cutting line BB. In this embodiment, the cover 6 has a lip 28 and the inlet channel 7 and the outlet channel 8, as well as a guide 29.

[0193] Figure 18b Shown Figure 17Schematic diagram of a cross-section of the flow sensor assembly taken along cutting line AA.

[0194] The lip 28 of the cover 6 increases the land area on the cover surface to improve the connection performance. The lip or lips 28 can have any shape and positioning that enhances the mechanical connection of the component to the system.

[0195] In this example, there are two guide structures 29 positioned on the lid 6. The guide structures 29 separate the flow channel into a flow sensing channel and two side channels 30. The flow sensing channel extends over the center of the flow sensor, and outside the flow sensing channel, the side channel flow 30 flows between the inlet channel 7 and the outlet channel 8. The guides 29 control and guide the flow through the package, which reduces turbulence in the flow sensing area. The guides can have any size or shape that helps control or layer the flow within the package. The side channels 30 allow space for wire bonding connections and limit any eddy currents generated from the inlet channel 7 away from the flow sensing tube core 1.

[0196] Figure 18c Computational fluid dynamics (CFD) simulations of exemplary cross sections of embodiments without guide structures are shown. Figure 18d As shown in Figure 18b Computational fluid dynamics (CFD) simulation of an exemplary cross section described in [1], wherein the device has a guide structure. The simulation shows the relative magnitude of the velocity as grayscale, with the velocity direction superimposed as a vector. It can be seen that in the embodiment with the guide structure, there is enhanced flow through the central channel and a significant reduction in vortices within the chamber.

[0197] Figure 19a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the guide 29 has a varying height. Figure 19b Shown Figure 19a 3D diagram of the interior design of a lid of an embodiment. The flow sensing lid 6 has side channels 30 and flow control guides 29 that extend through the fluid cavity and have varying heights. Guides 29 have a lower height near the inlet and outlet channels 7 and 8 and a greater height toward the center of the flow sensor assembly and above the flow sensor 1. In other words, guides 29 extend further from the lid 6 to the substrate 10 in the center of the flow sensor assembly than below the inlet and outlet channels 7 and 8.

[0198] During use, when fluid leaves the inlet channel 7, eddies are generated due to their circular shape exiting the inlet 7. The guide has a lower height near the inlet 7, allowing these eddies to enter the side channel and be directed downwardly along the side channel 30. The guide then becomes taller and thereby stops the interaction of these eddies in the flow sensing channel, thereby helping to create laminar flow over the flow sensing die 1.

[0199] Figure 20a and Figure 20b A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the cavity between the flow sensing die 1 and the edge 5 is filled with a filler material 11. The flow sensor assembly has a guide 29 similar to the guide of the flow sensor assembly of FIG18. Depending on the filler deposition method, the surface topography of the filler can be flat, concave, or convex. The filler material also protects the substrate bond pads and provides partial protection to the bond wires. The filler material forms a flat surface with the flow sensing surface and helps reduce discontinuities and flow separation caused by the edge of the flow sensing die.

[0200] Figure 21a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the cover includes a plenum or reservoir 31 where the flow can be dispersed, and guides 29 for protecting the flow sensing die from turbulence. Figure 21b Shown Figure 21a 3D diagram of the interior design of the lid of an embodiment of the present invention. The flow sensor assembly includes a flow sensing die 1, which includes a flow sensing surface 2, which includes a membrane 3. The flow sensing lid 6 includes a flow control guide 29 and a plenum 31.

[0201] Plenum 31 is a spatial region near or below inlet and outlet channels 7 and 8 where fluid flowing through the device can be dispersed. By using plenum 31 in conjunction with guide 29, system flow can be controlled. Plenum 31 diffuses fluid energy, while guide 29 protects the flow sensing element from eddies and turbulence generated by the fluid exiting the inlet.

[0202] Figure 22a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein guides 29 near the inlet 7 and outlet 8 are elevated above the center of the subassembly above the flow sensing die 1 . Figure 22b Shown Figure 22a 3D diagram of the lid interior design of an embodiment of FIG. There is filler material 11 in the cavity between the flow sensing die 1 and the substrate edge 5. The flow sensing lid 6 includes flow control guides at varying heights 29, side channels 30, and a plenum 31. Figure 22c Shown according to Figure 22aA schematic cross section along cutting line CC is shown illustrating the use of guide structures 29 to protect the bond wires.

[0203] In this embodiment, guides 29a near inlet 7 and outlet 8 are larger (taller and thicker) than guides 29b in the center of the subassembly above the flow sensing die 1. In other words, guides 29 extend further from lid 6 to substrate 10 below inlet 7 and outlet 8 channels than in the center of the flow sensor assembly. This means that the guides block more of the flow channel below inlet 7 and outlet 8 channels than above the flow sensing die 1.

[0204] When the guides 29 near the inlet 7 and outlet 8 are larger, the side channels are inaccessible to the flow flowing downward because there is no space between the filler material 11 and the cover 6. This embodiment creates a flow channel with a smaller cross-sectional area, improving the sensitivity of the device. Because the wire bonds are outside the flow sensing channel and in the side channels 30, this embodiment also ensures minimal fluid contact with the wire bonds and wire bond pads by preventing the fluid flow from passing through the side channels. This improves the life of the system by minimizing the effects of corrosion on the bond wires and bond pads.

[0205] Figure 23a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein there is no filling material in the cavity between the flow sensing die 1 and the substrate edge 5 . Figure 23b Shown Figure 23a 3D diagram of the interior design of the cover of an embodiment. The flow sensing cover 6 includes flow control guides 29 and plenum chambers 31 at varying heights.

[0206] This embodiment is geometrically similar to Figure 22a and Figure 22b 5 , except that there is no filler material between the flow sensing die 1 and the substrate rim 5. The absence of filler material creates an alternative path to access the side channels, allowing flow to exit the flow sensing channels below the guide structure 29 and flow around the sensing die 1. In this embodiment, flow eddies can enter the side channels around the flow sensing die 1 and in the cavity of the substrate 10 formed by the rim 5 and then be kept separate from the flow sensing surface via the guide 29, thereby promoting flow control and streamlines. In this case, the rim 5 has sloped sides and a rounded shape. The rim 5 may alternatively have vertical walls.

[0207] Figure 24a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the guide structure 29 is formed on the flow sensing die 1 instead of the cover 6 . Figure 24b Shown Figure 24a 3D diagram of the lid interior design of an example.

[0208] In this embodiment, the guide structures 29 are formed on the flow sensing die 1 rather than on the lid 6. If the guide structures were located on the lid, they would not contact the sensing die surface (the flow channel surface) during assembly. However, when the guides are manufactured on the flow sensing die, there will be no gap between the guides and the flow sensing surface. This provides the advantage of high-tolerance guides and means that there will be no gap between the flow sensing surface and the guides, resulting in a well-controlled flow channel.

[0209] Figure 25a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the cover 6 has a platform structure 32 extending downwardly from the cover 6 . Figure 25b Shown Figure 25a 3D diagram of the interior design of the lid of an embodiment. The flow sensing lid 6 includes flow control guides 29 at varying heights and a platform structure 32 that extends downward from the lid 6 and can contact the flow sensing die 1 within the assembly.

[0210] In this embodiment, a platform structure 32 is formed on the lid 6. When the system is assembled, the platform structure 32 can be used to contact the flow sensing die 1, thereby providing the benefit of greater tolerance control of the height of the flow sensing channel, which directly leads to better repeatability. In addition, the platform structure provides a minimum height for the wire bonding ring height (when in contact), thereby forming a system in which the lid 6 does not interfere with the wire bonding.

[0211] Figure 26a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein the flow sensor assembly has a platform structure 32 formed on a cover 6 and a flow sensing die 1 . Figure 26b Shown Figure 26a 3D representation of .

[0212] This embodiment is similar to Figure 25a and 25b However, in this embodiment, the flow sensing die 1 has an additional platform structure 32 on the side adjacent to the cover 6 that serves as a platform structure. Figure 26a In, as in Figure 26b As can be seen in the 3D representation of FIG, two platform structures 32 are positioned on either side of the flow channel. Such structures can contact the cover 6 within the assembly or contact the platform structure 32 also placed on the cover 6. Such structures will allow for more precise control of the tolerance of the channel height and help avoid assembly breakage.

[0213] Figure 27aA schematic cross-section (taken along line BB) of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein an additional temperature sensing element is positioned outside of the flow control guide structure. Figure 27b Shown along Figure 27a . The flow sensor assembly includes a flow sensing die 1 including a flow sensing element 22 and a temperature sensing element 33, and a flow sensing surface 2 including a membrane 3. The flow sensing cover 6 includes a flow control guide 29. The cavity between the flow sensing die 1 and the edge 5 is filled with a filler material 11. The flow sensor assembly also includes a side channel 30.

[0214] The flow sensing element of flow sensing die 1 is contained within the flow sensing channel between two flow control guide structures 29. However, the additional temperature sensing element 33 is positioned outside the flow control guide structures and not within the flow sensing channel. In this embodiment, filler material 11 renders the side channels inaccessible, thus meaning that no flow enters the side channels 30. This results in the reference temperature measuring the true ambient temperature and being less affected by flow.

[0215] Figure 28a A schematic cross-section of a flow sensor assembly according to an embodiment of the present disclosure is shown, wherein a guide structure 29 protrudes vertically in the center of the flow sensor assembly and contacts the flow sensing surface 2 . Figure 28b Shown Figure 28a 3D illustration of the interior design of the lid of an embodiment. This embodiment shows a flow sensor assembly including a flow sensing die 1, which includes a flow sensing surface 2, which includes a membrane 3. The flow sensing lid 6 includes side channels 30 and flow control guides 29, which extend through the fluid cavity and have varying heights. Guide structures 29 protrude vertically from the center of the flow sensor assembly and contact the flow sensing surface 2, creating a closed fluid chamber above the flow sensing die 1 and the flow sensing channel.

[0216] In this embodiment, the guide structure 29 contacts the flow sensing die 1 and completely separates the flow sensing channel from the side channel 30. This results in any side channel eddy currents not being able to negatively impact the flow over the flow sensing die 1 within the flow sensing channel.

[0217] Figure 29 A 3D diagram of a flow sensor assembly according to an embodiment of the present disclosure is shown. This embodiment shows a flow sensor assembly comprising a substrate 10, a cover 6 comprising a lip 28, an inlet channel 7 and an outlet channel 8. This embodiment also comprises a gasket 34.

[0218] In this embodiment, a gasket 34 is placed around the inlet channel 7 and the outlet channel 8 and contacts the outer surface of the flow sensor assembly cover 6. When the flow sensor assembly is connected to a system for use therewith, the gasket 34 will be compressed between the cover 6 and the adjacent system and provide an airtight seal between the flow sensor assembly and the fixture used therewith.

[0219] Figure 30 A 3D diagram of a flow sensor assembly according to an embodiment of the present disclosure is shown. This embodiment shows a flow sensor assembly comprising a package 10, a cover 6 comprising a lip 28, an inlet channel 7, and an outlet channel 8. This embodiment also comprises a gasket 34 and an adhesive layer or tape 35.

[0220] In this embodiment, in addition to the gasket 34, there is a pressure sensitive adhesive tape 35. The tape is used to help form an airtight seal between the flow sensor assembly cover 6 and the gasket 34, and also ensures that the gasket remains attached to the flow sensor assembly through in situ measurements.

[0221] Those skilled in the art will understand that in the preceding description and the appended claims, positional terms such as "above," "overlapping," "below," and "lateral" are used with reference to conceptual illustrations of the device, such as those showing standard cross-sectional perspective views and those shown in the accompanying drawings. These terms are used for ease of reference and are not intended to be limiting. Therefore, these terms should be understood to refer to the device when in the orientation shown in the accompanying drawings.

[0222] Although the present invention has been described in terms of the preferred embodiments described above, it should be understood that these embodiments are illustrative only and that the claims are not limited to these embodiments. In light of this disclosure, those skilled in the art will be able to make modifications and substitutions, which are considered to fall within the scope of the appended claims. Each feature disclosed or illustrated in this specification may be incorporated into the present disclosure alone or in any appropriate combination with any other features disclosed or illustrated herein.

[0223] Many other effective alternatives will occur to those skilled in the art.It should be understood that the present disclosure is not limited to the embodiments described, but covers all modifications that fall within the spirit and scope of the present disclosure.

Claims

1. A flow sensor assembly comprising: a first substrate; a flow sensor positioned on a first substrate; a cover positioned over the sensor; flow inlet channels; outflow channel; a flow sensing channel located between the flow inlet channel and the flow outlet channel; and one or more guide structures, wherein the guide structures are coupled to the cover and extend partially downwardly toward the flow sensor to at least partially separate the flow sensing channel from one or more regions between the flow inlet channel and the flow outlet channel outside the flow sensing channel, and A surface of the flow sensor, a surface of the cover, and surfaces of the one or more guide structures cooperate to form the flow sensing channel.

2. The flow sensor assembly according to claim 1, wherein The one or more guide structures include one or more protrusions on an inner surface of the cover.

3. The flow sensor assembly according to claim 1 or 2, wherein: The one or more flow sensing channels are over a center of the flow sensor, and wherein the one or more regions include one or more side channels surrounding the flow sensor.

4. The flow sensor assembly according to claim 1 or 2, wherein: The flow sensor assembly includes a bond wire electrically connected to the flow sensor, and wherein the guide structure separates the bond wire from the flow sensing channel.

5. The flow sensor assembly of claim 1 or 2, further comprising a gasket, wherein an outer surface of the cover abuts the gasket.

6. The flow sensor assembly of claim 5, wherein: The assembly also includes an adhesive layer between the gasket and the cover.

7. The flow sensor assembly of claim 1 or 2, wherein the one or more guide structures have a non-uniform height along the flow channel.

8. The flow sensor assembly of claim 7, wherein: The one or more guide structures have a first height near the inlet and outlet channels, the first height being lower than a second height of the one or more guide structures near the flow sensor toward the center of the flow sensor assembly.

9. The flow sensor assembly of claim 7, wherein: The one or more guide structures have a relatively greater height in a region close to the inlet channel.

10. The flow sensor assembly of claim 9, wherein: The bottom surface of the flow sensing channel is formed by the flow sensor in combination with a filling material; the top surface of the flow sensing channel is formed by the cover; and one or more side walls of the flow sensing channel are formed by the guide structure.

11. The flow sensor assembly of claim 1 or 2, wherein the guide structure does not contact the flow sensor. 12 . The flow sensor assembly of claim 1 , wherein the guide structure is configured to isolate eddy currents from the flow sensing channel.

13. A method of manufacturing a flow sensor assembly, the method comprising: forming a first substrate; forming a flow sensor on a first substrate; forming a cover over the flow sensor; forming an inlet channel; Forming an outflow channel, forming a flow sensing channel between the flow inlet channel and the flow outlet channel; forming one or more guide structures, wherein the guide structures are coupled to the cover and extend partially downwardly toward the flow sensor to at least partially separate the flow sensing channel from one or more regions between the flow inlet channel and the flow outlet channel outside the flow sensing channel; Wherein a surface of the flow sensor, a surface of the cover, and surfaces of the one or more guide structures cooperate to form the flow sensing channel.

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