U.S. patent application number 17/726449 was filed with the patent office on 2022-08-04 for sensor assembly.
The applicant listed for this patent is Flusso Limited. Invention is credited to Andrea DE LUCA, John Charles JOYCE, Cerdin LEE, Christopher James ROSSER.
Application Number | 20220244083 17/726449 |
Document ID | / |
Family ID | 1000006343235 |
Filed Date | 2022-08-04 |
United States Patent
Application |
20220244083 |
Kind Code |
A1 |
DE LUCA; Andrea ; et
al. |
August 4, 2022 |
SENSOR ASSEMBLY
Abstract
A flow sensor assembly comprising a first substrate, a flow
sensor located over the first substrate, a lid located over the
first substrate and the flow sensor, a flow inlet channel, a flow
outlet channel, and an overmold laterally encircling the flow
sensor. The overmold is in contact with the side walls of the flow
sensor, and extends between the flow sensor and the lid such that
the overmold, the flow sensor, and the lid define a flow sensing
channel between the flow inlet channel and the flow outlet channel.
the lid and the encapsulation cooperate to define the flow inlet
channel and the flow outlet channel.
Inventors: |
DE LUCA; Andrea;
(Cambridgeshire, GB) ; JOYCE; John Charles;
(Cambridgeshire, GB) ; LEE; Cerdin;
(Cambridgeshire, GB) ; ROSSER; Christopher James;
(Cambridgeshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Flusso Limited |
Cambridgeshire |
|
GB |
|
|
Family ID: |
1000006343235 |
Appl. No.: |
17/726449 |
Filed: |
April 21, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/EP2020/078299 |
Oct 8, 2020 |
|
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17726449 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01F 1/6842 20130101;
G01F 1/6847 20130101 |
International
Class: |
G01F 1/684 20060101
G01F001/684 |
Claims
1. A flow sensor assembly comprising: a first substrate; a flow
sensor located over the first substrate; a lid located over the
first substrate and the flow sensor; a flow inlet channel; a flow
outlet channel; and an overmold laterally encircling the flow
sensor and in contact with the side walls of the flow sensor,
wherein the overmold extends between the flow sensor and the lid
such that the overmold, the flow sensor, and the lid define a flow
sensing channel between the flow inlet channel and the flow outlet
channel, and wherein the lid and the encapsulation cooperate to
define the flow inlet channel and the flow outlet channel.
2. A flow sensor assembly according to claim 1, wherein the flow
sensing channel comprises sloped sidewalls formed by the overmold;
and/or wherein the overmold is disposed at least partly over a top
surface of the flow sensor.
3. A flow sensor assembly according to claim 1, further comprising
electrical contacts coupling the flow sensor to the first
substrate, and wherein the electrical contacts are encapsulated
within the overmold.
4. A flow sensor assembly according to claim 1, wherein a first
surface of the overmold is substantially level with a surface of
the sensor.
5. A flow sensor assembly according to claim 1, wherein the flow
channel comprises one or more channel restrictors, and optionally
wherein the one or more channel restrictors is located above the
flow sensor.
6. A flow sensor assembly according to claim 1, further comprising
one or more guide structures located between the flow inlet channel
and the flow outlet channel.
7. A flow sensor assembly according to claim 1, wherein the lid
comprises a recess, and wherein the recess, the overmold, and the
flow sensor define the flow channel through the flow sensor
assembly.
8. A flow sensor assembly according to claim 1, further comprising
an additional flow channel formed by at least one further recess or
aperture within the overmold and/or the lid; and optionally wherein
said additional flow channel is substantially parallel to the flow
sensing channel; and/or wherein said additional flow channel has a
substantially larger cross-sectional area than the flow sensing
channel.
9. A flow sensor assembly according to claim 1, wherein the
overmold and/or the lid are configured such that the flow inlet
channel and/or the flow outlet channel have a larger cross-section
than the flow sensing channel, and optionally wherein a
cross-sectional area of the flow inlet channel and/or the flow
outlet channel tapers from a surface of the flow sensor assembly
towards the flow sensing channel.
10. A flow sensor assembly according to claim 1, further comprising
one or more spacers having a first surface located within 50 .mu.m
of a surface of the flow sensor or a surface of the first
substrate, and a second surface in contact with a first surface of
the lid, wherein the first surface of the lid faces the flow sensor
and the first substrate.
11. A flow sensor assembly comprising: a first substrate; a flow
sensor mounted on a first surface of the first substrate; a lid
located over the first substrate and the flow sensor; a flow inlet
channel; a flow outlet channel, wherein a surface of the flow
sensor and a surface of the lid cooperate to form a flow sensing
channel between the flow inlet channel and the flow outlet channel;
and a spacer having: a first surface located within 50 .mu.m of a
surface of the flow sensor or a surface of the first substrate; and
a second surface in contact with a first surface of the lid,
wherein the first surface of the lid faces the flow sensor.
12. A flow sensor assembly according to claim 11, wherein the first
surface of the spacer is in contact with a top surface of the flow
sensor or a top surface of the first substrate, and wherein the top
surface of the flow sensor or the top surface of the first
substrate faces the lid.
13. A flow sensor assembly according to claim 11, wherein a second
surface of the lid is in contact with a second surface of the first
substrate, by way of an adhesive, and wherein the second surface of
the lid faces the same direction as the first surface of the lid;
and optionally wherein the second surface of lid comprises one or
more recesses configured to receive the adhesive; and optionally
wherein one or more recesses comprise an aperture within a sidewall
of the recess.
14. A flow sensor assembly according to claim 11, wherein the first
surface of the spacer is in contact with a top surface of the flow
sensor, wherein the top surface of the flow sensor faces the lid,
and wherein a bottom surface of the flow sensor is in contact with
the first surface of the first substrate, by way of an adhesive,
wherein the first surface of the first substrate faces the lid.
15. A flow sensor assembly according to claim 11, wherein the one
or more spacers extend from a first inside edge of the lid to a
second inside edge of the lid; and/or wherein the one or more
spacers is monolithic with the lid
16. A flow sensor assembly according to claim 11, wherein the one
or more spacers is configured to be within 50 .mu.m of at least one
side surface of the flow sensor; and optionally wherein the one or
more spacers is in contact with at least one side surface of the
flow sensor; and/or wherein the first surface of the one or more
spacer is chamfered.
17. A flow sensor assembly according to claim 1, wherein the flow
sensor comprises: a sensor substrate comprising an etched portion;
a dielectric layer located on the sensor substrate, wherein the
dielectric layer comprises at least one dielectric membrane located
over the etched portion of the sensor substrate; and a sensing
element located on or within the dielectric membrane; and
optionally wherein the first substrate defines an aperture.
18. A flow sensing system comprising: a main channel extending in a
first direction; a flow sensor assembly according to claim 1,
wherein the flow sensor assembly is located in the main channel
such that the flow sensing channel of the flow sensor assembly is
substantially parallel to the main channel.
19. A method of manufacturing a flow sensor assembly, the method
comprising: forming a first substrate; forming a flow sensor
located over the first substrate; forming a lid located over the
first substrate and the flow sensor; forming a flow inlet channel;
forming a flow outlet channel; forming an overmold laterally
encircling the flow sensor and in contact with the side walls of
the flow sensor, wherein the overmold extends between the flow
sensor and the lid such that the overmold, the flow sensor, and the
lid define a flow sensing channel between the flow inlet channel
and the flow outlet channel, and wherein the lid and the
encapsulation cooperate to define the flow inlet channel and the
flow outlet channel.
20. A method of manufacturing a flow sensing system, the method
comprising: providing a main channel extending in a first
direction; manufacturing a flow sensor assembly according to the
method of claim 19; positioning the flow sensor assembly within the
main channel such that the flow sensing channel of the flow sensor
assembly is substantially parallel to the main channel.
Description
TECHNICAL FIELD
[0001] The present application relates to a fluid flow sensor
assembly and a method of manufacturing a fluid flow sensor
assembly.
BACKGROUND
[0002] Thermal fluid flow sensors utilise the thermal interaction
between the sensor itself and the fluid. Generally, a flow sensor
assembly comprises a sensing die, a substrate, and a housing. In
most cases, the housing comprises a flow channel with an inlet and
an outlet. Electrical connections (e.g. bond wires) to the flow
sensing die are often used. The channel is a fluidic element
responsible for driving the fluid across the sensing die. The
design of the flow channel strongly affects the performance of the
flow sensing assembly (e.g. range, accuracy, noise, etc.).
[0003] In most electronic devices and sensors, the positioning of
the package lid with respect to the device chip is not critical as
long as the lid protects the device. However, in the case of flow
sensors where the lid is an important part of the flow path, small
misalignments between the lid and chip can affect the flow speed
seen by the sensor chip and will affects its sensitivity and
performance.
[0004] U.S. Pat. No. 10,151,612, EP 3032227, and U.S. Pat. No.
10,345,131 describe overmolded flow sensors. US 2014/0311912
describes modular microfluidic channel structures. US 2018/0172493,
U.S. Pat. Nos. 4,548,078, 8,418,549, 8,695,417, 9,091,577, and
9,003,877 describe flow sensor assemblies.
SUMMARY
[0005] Aspects and preferred features are set out in the
accompanying claims.
[0006] According to a first aspect of the disclosure, there is
provided a flow sensor assembly comprising: [0007] a first
substrate; [0008] a flow sensor located over the first substrate;
[0009] a lid located over the first substrate and the flow sensor;
[0010] a flow inlet channel; [0011] a flow outlet channel; [0012]
an overmold laterally encircling the flow sensor and in contact
with the side walls of the flow sensor, wherein the overmold
extends between the flow sensor and the lid such that the overmold,
the flow sensor, and the lid define a flow sensing channel between
the flow inlet channel and the flow outlet channel.
[0013] The flow sensor assembly may comprise a first substrate, a
flow sensor located over the first substrate having a top surface
comprising a flow sensing area, an encapsulation partially
encapsulating the flow sensor and leaving at least the flow sensing
area exposed, and a lid located over the encapsulation having a
surface in contact with the encapsulation. The flow sensor assembly
may also have first and second sides perpendicular to the top
surface of the flow sensor, where the first and second sides may
have at least one opening between the lid and encapsulation, or
between the substrate and lid, and a first flow channel between
these two openings. The fluid flow going through the first flow
channel is referred to as `flow.sub.se` and has a direction
substantially parallel with the flow sensor top surface.
[0014] The overmold may also be referred to as an encapsulation.
The flow sensing channel may extend in a first direction, laterally
through the flow sensor assembly and parallel to a top surface of
the flow sensor. The overmold may be a polymer material, for
example, an epoxy.
[0015] The flow sensing channel may extend laterally through the
device providing a fluid flow path laterally through the sensor
assembly, past the flow sensor. A top surface of flow sensor may
define a lower surface of the flow sensing channel.
[0016] The flow inlet channel, the flow outlet channel and the flow
sensing channel together form the flow channel. The flow sensing
channel may be defined as the whole length of the portion of the
flow channel between the flow inlet channel and the flow outlet
channel.
[0017] The lid and the encapsulation cooperate to define the flow
inlet channel and the flow outlet channel. In other words, the flow
inlet channel and the flow outlet channel may be defined by the
cooperation of the shapes of the first substrate and the lid,
and/or defined as a region between the first substrate and the lid
either side of the flow sensing channel.
[0018] The flow inlet channel and the flow outlet channel may be
defined on at least one surface of the flow sensor assembly,
wherein the at least one surface is perpendicular to the top
surface of the flow sensor. The flow inlet channel and the flow
outlet channel may be defined on opposite surfaces of the flow
sensor assembly. In other words, the flow inlet channel and flow
outlet channel may be on opposite sides of the flow sensor such
that fluid travels in one direction through the sensor. Fluid
enters in same direction as it leaves, and therefore the sensor can
be used in a continuous flow.
[0019] Alternatively, the flow inlet channel and the flow outlet
channel may be defined on adjacent sides of the flow sensing
assembly. The adjacent sides may be perpendicular to each
other.
[0020] The flow sensing channel may comprise sloped sidewalls
formed from the overmold. The sloped sidewalls may be sloped in
relation to a lower surface of the flow sensing channel.
[0021] The overmold may be disposed at least partly over a top
surface of the flow sensor.
[0022] The overmold may be configured such that a surface of the
flow sensing channel is substantially flat in one direction between
the flow inlet channel and the flow outlet channel. In use, once
flow has passed through the flow inlet channel it reaches the flow
sensing channel which may have a substantially flat surface. As a
surface of the flow sensing channel may be substantially flat, the
fluid flow through the flow sensing channel may flow parallel to
the surface of the flow sensing channel and hits no or a reduced
number of disturbances such as corners of the flow sensor (flow
sensing die) within the flow sensing channel. The device therefore
reduces turbulence through the sensor assembly, in particular
around a flow sensing surface of the flow sensor, and improves the
functionality of the flow sensor assembly.
[0023] As the overmold is at least partly disposed over a top
surface of the flow sensor, it covers the corners of the flow
sensor. Disturbances such as the corners of the flow sensor may be
present are therefore not located within the flow sensing channel,
and therefore do not increase turbulence in the flow sensing
channel.
[0024] The surface of the flow sensing channel that is flat may be
a first surface closest to the first substrate and defined by the
flow sensor and the overmold. The surface that is substantially
flat may include the surface of the flow sensor and a region of the
flow sensing channel surface around the flow surface. Therefore,
the surface of the flow sensor may be flush or level with the
surface of the region around the flow sensor.
[0025] Alternatively, the surface that is substantially flat may be
a second surface furthest from the first substrate and defined by
the lid. Both the first and second surfaces of the flow sensing
channel may be substantially flat to reduce turbulence.
[0026] The flow sensor assembly provides a miniature fluid flow
sensor assembly manufacturable in very high volumes at low unit
cost, whereby the onset of turbulences is reduced in proximity to
the flow sensing structure to increase the flow sensing performance
while maintaining a miniaturised form factor.
[0027] The flow sensor assembly may further comprise electrical
contacts, such as bond pads and bond wires, coupling the flow
sensor to the first substrate. The electrical contacts may be
encapsulated within the overmold.
[0028] A first surface of the overmold may be substantially level
with a top surface of the flow sensor. A lower surface of the flow
sensing channel may be substantially flat through the length of the
flow sensing channel.
[0029] The flow sensor assembly may comprise one or more structures
configured to manipulate `flow.sub.se` by engineering the flow
sensing channel cross-sectional area along the channel length to
improve the flow sensor assembly performance in terms of size,
weight, sensitivity, accuracy, dynamic range, particles resilience,
and/or robustness.
[0030] The flow channel may comprise one or more channel
restrictors.
[0031] Restrictors may be placed at the flow inlet and flow outlet
to reduce the effect on the flow sensing performance of the flow
sensor assembly when integrated into the system using it.
Restrictors may also be placed along the flow sensing channel in
proximity of the flow sensing surface of the flow sensor to locally
increase the flow speed and thus improve the flow sensing
performance.
[0032] The one or more restrictors may be located on the lid. The
restrictor may be configured to manipulate `flow.sub.se`. The
restrictor may be located above the flow sensor to reduce the cross
sectional area of the flow sensing channel in a region directly
above the flow sensor, resulting in an `flow.sub.se` velocity
increase.
[0033] Alternatively, or additionally, the flow channel may
comprise one or more protrusions located directly on and above the
overmold and laterally spaced from the flow sensor. The protrusions
may be monolithic with the overmold. The protrusions cause a
localised increase of flow velocity in the region close to the
protrusion. The protrusions may be located such that once the flow
passes the protrusion and reaches the flow sensor (where
cross-section area is larger), the flow will again slow down. The
protrusion makes the flow better conditioned, for example it
reduces flow turbulence, prior to the flow reaching the flow
sensor. The protrusions thus improve or condition the flow before
it reaches the flow sensing channel.
[0034] The flow sensor assembly may further comprise one or more
guide structures located between the flow inlet channel and the
flow outlet channel. The one or more guide structures may be
located on or monolithic with the lid. The one or more guide
structures may comprise one or more protrusions on an inner surface
of the lid. The guide structures may be incorporated into or formed
on a roof of the flow channel, that is provided by the lid. When
incorporated into the lid, the guide structures may or may not
extend down and contact the flow sensor or the encapsulation,
forming a sealed channel.
[0035] The guide structures may at least partially separate the
flow sensing channel from one or more regions between the inlet
channel and outlet channel outside the flow sensing channel. The
guide structures may be configured to separate the flow channel
into one or more extra flow channels, with the flow sensing channel
above the centre of the flow sensor, and one or more side channels
laterally spaced from the flow sensor.
[0036] The guide structures may extend along a length of the flow
sensing channel. The guide structures improve control of
`flow.sub.se` direction.
[0037] The lid may comprise a recess. The recess may be located on
a first surface of the lid, wherein the first surface of the lid
faces the flow sensor. The recess, the overmold, and the flow
sensor may define the flow channel through the flow sensor
assembly. Sidewalls of the recess of the lid may correspond with
the sidewalls of the overmold. The recess increases the
cross-sectional area of the channel, so that when the flow sensor
assembly is placed within a much larger main channel, a larger
proportion of the flow goes through the flow sensor assembly
thereby improving sensor performance.
[0038] The flow sensor assembly may further comprise an additional
flow channel formed by at least one further recess or aperture
within the overmold and/or the lid. The flow sensor assembly may
have first and second sides perpendicular to the top surface of the
flow sensor. The first and second sides may have multiple openings
between the lid and the encapsulation, or between the substrate and
the lid, forming multiple flow channels between the multiple
openings. The additional flow channels may include one or more
structures configured to manipulate the flow within the additional
flow channels.
[0039] The additional flow channel may be substantially parallel to
the flow sensing channel. The flow sensor assembly may further
comprise fins located within the additional flow channel.
[0040] The additional flow channel may be in a same plane as the
flow sensing channel.
[0041] The additional flow channel and the flow sensing channel may
both be connected to the same flow inlet channel and the same flow
outlet channel. A portion of the fluid flow entering the flow inlet
channel may travel directly through the additional channel instead
of the flow sensing channel, bypassing the flow sensing
channel.
[0042] The additional channel may have a larger cross-sectional
area than the flow sensing channel and may directly extend between
the flow inlet channel and the flow outlet channel. The flow
sensing channel may be connected to the additional channel and may
be parallel to the additional channel. In this instance, the
additional channel may be referred to as a main channel and the
flow sensing channel may be referred to as a bypass channel.
[0043] The additional flow channel may include one or more
structures configured to manipulate the flow within the additional
flow channels. The one or more structures configured to manipulate
the flow may be either part of the lid or part of the
encapsulation. Some examples of features are restrictors, guides,
pressure drop elements, deflection fins, and additional in-plane or
our-of-plane openings.
[0044] The additional flow channel may have a substantially larger
cross-sectional area than the flow sensing channel.
[0045] The additional flow channel may be located above the flow
sensing channel. The additional flow channel may be not located in
the same plane as the flow sensing channel, and may be referred to
as an out-of-plane bypass structure.
[0046] The overmold and/or the lid may be configured such that the
flow inlet channel and/or the flow outlet channel have a larger
cross-section than the flow sensing channel. A cross-sectional area
of the flow inlet channel and/or the flow outlet channel tapers
from a surface of the flow sensor assembly towards the flow sensing
channel. The flow channel of the flow sensor assembly may have a
tapered cross sectional area that is wider at the open ends of the
flow inlet channel and the flow outlet channel, and is narrower in
the flow sensing channel. The encapsulation, the lid, or both the
encapsulation or the lid may have features adjacent to the open
ends of the flow inlet channel and the flow outlet channel to
provide a funnel shaped structure.
[0047] The flow sensor assembly may further comprise one or more
spacers having a first surface located within 50 .mu.m of, and more
preferably in contact with, a surface of the flow sensor or a
surface of the first substrate. The one or more spacers may have a
second surface in contact with a first surface of the lid, wherein
the first surface of the lid faces the flow sensor and the first
substrate.
[0048] According to a further aspect of the disclosure, there is
provided a flow sensor assembly comprising: [0049] a first
substrate; [0050] a flow sensor mounted on a first surface of the
first substrate; [0051] a lid located over the first substrate and
the flow sensor; [0052] a flow inlet channel; [0053] a flow outlet
channel, wherein a surface of the flow sensor and a surface of the
lid cooperate to form a flow sensing channel between the flow inlet
channel and the flow outlet channel; and [0054] a spacer having:
[0055] a first surface located within 50 .mu.m of a top surface of
the flow sensor or a top surface of the first substrate, wherein
the top surface of the flow sensor or the first substrate faces the
lid; and [0056] a second surface in contact with a first surface of
the lid, wherein the first surface of the lid faces the flow
sensor.
[0057] The flow sensor assembly may comprise a flow sensor chip on
a package substrate, and a lid covering the package substrate,
where the lid forms part of the flow channel. The flow sensor
assembly may comprise structures to ensure alignment of the lid to
the sensor chip and/or the package substrate. The alignment
structures can be for horizontal, vertical, and/or rotational
alignment. Preferably the alignment ensure horizontal, vertical,
and rotational alignment. The purpose of ensuring alignment is to
improve consistency of the geometry of the flow path for the fluid
being sensed, and thus improve consistency of performance between
different sensors. The alignment structures could also be combined
with, or incorporated into, flow and/or vortex guides.
[0058] The first surface of the spacer may be in contact with a top
surface of the flow sensor or a top surface of the first substrate,
and the top surface of the flow sensor or the top surface of the
first substrate may face the lid.
[0059] The flow sensor assembly may comprise: a first substrate; a
flow sensor located over the first substrate; a lid located over
the flow sensor; a flow inlet channel; a flow outlet channel,
wherein a surface of the flow sensor and a surface of the lid
cooperate to form a flow sensing channel between the flow inlet
channel and the flow outlet channel; and wherein there are
alignment structures to improve alignment and positioning of the
lid with respect to either the flow sensor and/or the first
substrate.
[0060] As the lid of the flow sensor assembly defines the flow
sensing channel, misalignments between the lid and chip can affect
the flow speed seen by the sensor chip and will affects its
sensitivity and performance. The use of alignment structures
therefore can help to align the lid better during the packaging
process, resulting in better device performance, and better
reproducibility from device to device.
[0061] The alignment structures may be configured to improve
vertical alignment, horizontal alignment, or rotational alignment.
Vertical alignment can be improved by use of structures that extend
from the lid to the top of the sensor chip or to the first
substrate. In package assembly, the lid may be lowered until these
structures touch the sensor chip or the first substrate. Horizontal
alignment can be improved by having structures with corner or side
brackets in the lid that align with the corners or sides of the
flow sensor. Such structures will also provide rotational
alignment. During assembly of the flow sensor assembly, an optical
method may be used to ensure alignment of the lid to the flow
sensor, or the lid may be moved until it drops into place. A device
may have only vertical alignment structures, or only horizontal
alignment structures, or may comprise separate structures for
vertical and horizontal alignment, or structures that provide the
function of both vertical and horizontal alignment.
[0062] The lid may laterally encircle the flow sensor.
[0063] A second surface of the lid may be in contact with a second
surface of the first substrate, by way of an adhesive. The second
surface of the lid may face the same direction as the first surface
of the lid. The second surface of the first substrate may face the
same direction as the first direction of the first substrate.
[0064] The second surface of lid may comprise one or more recesses
configured to receive the adhesive.
[0065] The first surface of the spacer may be in contact with a top
surface of the flow sensor, wherein the top surface of the flow
sensor faces the lid. A bottom surface of the flow sensor may be in
contact with the first surface of the first substrate, by way of an
adhesive, wherein the first surface of the first substrate faces
the lid.
[0066] The one or more spacers may extend from a first inside edge
of the lid to a second inside edge of the lid. The one or more
spacers may extend across an entire width of the internal volume of
the flow sensor assembly in a second direction. The one or more
spacers may define the flow sensing channel between the flow inlet
channel and the flow outlet channel.
[0067] The one or more spacers may be configured to be located
within 50 .mu.m of, and more preferably in contact with, at least
one side surface of the flow sensor. The first surface of the one
or more spacers may be chamfered. Alternatively, a surface of the
one or more spacers that is perpendicular to the first spacer may
be chamfered.
[0068] The one or more spacers may be in direct contact with the
flow sensor, alternatively the spacer may not be in direct contact
with the flow sensor assembly but may be located within a distance
of 50 .mu.m of at least one side surface of the flow sensor. This
allows for manufacturing tolerances of the spacers and the flow
sensing die.
[0069] The one or more spacers or alignment structures may act as
guide structures and may completely separate or isolate the flow
sensing channel from the one or more regions or additional flow
channels between the inlet channel and outlet channel outside the
flow sensing channel. The flow sensor assembly may comprise bond
wires electrically connected to the flow sensor, and the alignment
structures may separate the bond wires from the flow sensing
channel. The bond wires may be located in the one or more regions
between the inlet channel and outlet channel outside the flow
sensing channel.
[0070] The flow sensor assembly may further comprise one or more
extension members laterally adjacent to 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
extended portions of the flow sensor itself.
[0071] One or more of the flow inlet channel, the flow outlet
channel, or the flow sensing channel may comprise one or more
channel restrictors. The channel restrictors may be formed at any
location within the flow channel. The term `channel restrictors` is
used to refer to restrictors located within the flow channel.
[0072] The flow sensing channel guiding the fluid from the inlet to
the outlet results from the assembly of the lid on top of the
substrate. The bottom face (or first surface) of the flow sensing
channel may be formed by the extension member (which can be a
filler material) and the flow sensing surface of the flow sensing
die. Bond wires may be perpendicular to the fluid flow and
positioned in such a way to reduce their interaction with the fluid
flow and thus reduce the onset of unwanted turbulences.
[0073] The flow channel may have any cross-sectional geometry (e.g.
square, rectangular, semi-circular, irregular etc.). The
cross-section geometry may also vary along the length of the flow
channel (e.g. the cross-section of the flow channel may be circular
at the inlet and square at the flow sensing die section of the flow
sensing channel).
[0074] A specific case of non-uniform flow channel cross-sectional
area is using restrictors (i.e. the flow channel cross-sectional
area is locally reduced). Restrictors may be placed at the flow
inlet and flow outlet to reduce the effect on the flow sensing
performance of the flow sensor assembly when integrated into the
system using it. Restrictors may also be placed along the flow
sensing channel in proximity of the flow sensing surface of the
flow sensing die to locally increase the flow speed and thus
improve the flow sensing performance.
[0075] Another specific case of non-uniform flow channel
cross-sectional area is using reservoirs or plenums (i.e. the flow
channel cross-sectional area is locally enlarged).
[0076] Reservoirs may also be placed at the flow inlet and flow
outlet or along the flow sensing channel. By using plenums, at the
point at which the flow inlet and/or flow outlet meet the flow
sensing channel, there is a region within the flow inlet and/or
flow outlet channel that has a much larger cross-sectional area
than the remaining portion of the flow inlet/outlet channel.
Plenums may be placed at either the flow inlet or flow outlet or
both.
[0077] Also, 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 engineered to improve flow
sensor assembly performance.
[0078] The extension member may comprise a filler material adjacent
to the flow sensor and on the first substrate. The filler material
or gel may extend across a remaining width of the flow sensing
channel where the flow sensor is not present, and may have a
substantially flat top surface across the width of the flow sensing
channel. The filler material may extend to substantially the same
height above the first substrate as the flow sensor height above
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) across 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 one flat surface
throughout the entire length of the flow sensing channel.
[0079] 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 lid, or may be a separate component of the
flow sensor assembly.
[0080] The substrate may comprise a rim; and the rim may be
integral part of the substrate. Alternatively, the rim may be an
integral part of the lid or an additional element assembled onto
the substrate as part of the flow sensor assembly process. As a
result, a cavity between the rim and the flow sensing die is
formed. To reduce turbulences in proximity to 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 also protects the substrate bond
pads and offers partial protection to the bond wires.
[0081] The shape of the rim may have sloping, vertical or backward
sloping side walls, as long as the cavity within the rim contains
the flow sensing die. The rim may circumnavigate the package and
may be done so using any shape (e.g. circular, square, oval, square
with rounded edges).
[0082] The filler material may be any material (e.g. a polymer,
more specifically a gel, a resin, an epoxy, a ceramic, a metal, a
semiconductor, or a combination of those) with suitable electrical,
thermal, mechanical and chemical properties. The filler material is
electrically insulating, thermally conductive, thermo-mechanically
stable (i.e. does not expand or contracts in time and/or when
exposed to varying temperatures), chemically stable (i.e. does not
absorb, adsorb, desorb molecules in time). The filler material may
be deposited (e.g. printed, syringe dispensed, sprayed, etc.) in
ways compatible with the other elements forming the flow sensing
assembly with high reproducibility. A curing step may be used to
change the phase of the filler from fluid to solid.
[0083] The filler material may be configured such that it does not
overlap an upper surface of the flow sensor. The filler material
may have a concave or convex meniscus due to surface tension.
[0084] Alternatively, the filler material may slightly overlap the
flow sensor when the flow sensor is heated up when in use. This may
be achieved using a filler material with a concave or convex
meniscus. Although the filler material may be configured to reduce
the overlap between the filler material and the flow sensor in this
case.
[0085] The flow sensor assembly may comprise bond wires
electrically connected to the flow sensor, and the filler material
may be configured to cover the bond wires. The filler material may
fully encapsulate the bond wires; this reduces turbulence due to
the bond wires. Alternatively, the filler material may partly
encapsulate the bond wires and the bond wires may be configured to
have reduced interaction with the fluid flow through the fluid flow
sensor assembly.
[0086] Due to surface tension effects, the filler material may
fully encapsulate the bond wires and the die bond PADs for extra
protection.
[0087] The extension member may comprise an extension portion of
the flow sensor. The extension portion may be an integral part of
the flow sensor. The extension portion can be a region of a
substrate and a dielectric layer, or could be other form of
extension portion of a different type of flow sensor without a
substrate and a dielectric layer.
[0088] The lid may define one or more apertures, and the flow inlet
channel may comprise a channel through one of the apertures. The
flow inlet channel may be configured to be substantially
perpendicular to the flow sensing channel, and the extension member
may extend underneath the flow inlet channel. The extension member
may extend along the entire width of the inlet channel. These
features allow fluid flow from the flow inlet channel to flow onto
a substantially flat surface without disturbances when reaching the
flow sensing channel.
[0089] Alternatively, or additionally the flow outlet channel may
comprise a channel through one of the apertures. The flow outlet
channel may be configured to be substantially perpendicular to the
flow sensing channel, and the extension member may extend
underneath the flow outlet channel.
[0090] A top surface of the lid may be substantially flat such that
the flow inlet channel and the flow outlet channel terminate on the
top surface of the lid. The top surface may be defined as the
exterior surface of the lid that extends in a lateral direction,
substantially parallel to the flow sensing channel. The apertures
or openings defining the flow inlet channel and the flow outlet
channel may be flat.
[0091] Alternatively, the lid may comprise one or more protrusions
on an outer surface of the lid, and the one or more apertures may
extend through one or more of the protrusions. The protrusions may
comprise hoses. The protrusions may extend away from the flow
sensing channel.
[0092] The protrusions may be substantially perpendicular to the
flow sensing channel, and the flow inlet channel and flow outlet
channel may then be substantially perpendicular to the sensing
channel. In this embodiment, fluid enters and exits the flow sensor
in opposite directions.
[0093] Alternatively, the protrusions may be substantially parallel
to the sensing channel, and the flow inlet channel and flow outlet
channel may then be substantially parallel to the sensing channel.
In this embodiment, fluid enters and exits the flow sensor in the
same direction.
[0094] The flow sensor assembly may comprise a lid with a flow
inlet and a flow outlet both comprising hoses to facilitate
mechanical connection to the system using it. Hoses may have any
geometry used to facilitate mechanical connection to the system
using the flow sensor assembly. For instance, the hoses may have
barbs, grooves, protrusions or a combination of those to enhance
friction with the pipes or any other mean connected to them. The
number, size and position within the flow sensor assembly of the
inlet and the outlet might vary depending on the application
requirements.
[0095] The first substrate and the lid may cooperate to define the
flow inlet channel and the flow outlet channel. In other words, the
flow inlet channel and the flow outlet channel may be defined by
the cooperation of the shapes of the first substrate and the lid,
and/or defined as a region between the first substrate and the lid
either side of the flow sensing channel.
[0096] The lid further may comprise a lid restrictor, and the
extension member may extend under the whole length of the lid
restrictor. The term lid restrictor' is used to refer to a
restrictor formed on the lid. The lid restrictor may be located on
a lower surface of the lid. The lower surface of the lid may be
defined as the surface of the lid that defines the flow sensing
channel and is on the interior of the flow sensor assembly.
[0097] The lid may comprise a restrictor, placed along the flow
channel in proximity of the flow-sensing surface of the flow sensor
to locally increase the flow speed and thus improve the flow
sensing performance. This may be used in applications where the
flow sensor assembly is soldered on a surface over which a fluid is
flowing, and the application requires measuring a property of the
flowing fluid. This may be used in embodiment with a rim and filler
material, or in embodiments where the extension member is an
extended portion of the flow sensor.
[0098] The flow sensor assembly may further comprise an integrated
circuit or circuitry located between the flow sensor and the first
substrate. In other words, the first substrate, the integrated
circuit, and the flow sensor may be formed in a stack in the order
of first substrate, integrated circuit and flow sensor. In
embodiments with filler material, the filler material may
encapsulate the integrated circuit.
[0099] The flow sensor assembly may further comprise an integrated
circuit or circuitry located laterally spaced from the flow sensor
and over the first substrate, wherein the one or more extension
members covers the integrated circuitry. In other words, the flow
sensor and the integrated circuitry may be located side-by-side on
the first substrate. The extension member may fully cover the
integrated circuitry. In embodiments with filler material, the
filler material may encapsulate the integrated circuit.
[0100] The flow sensor assembly may also comprise an integrated
circuit (IC) die. The flow sensor may be stacked on top of the IC
die to reduce the overall flow sensor assembly form factor.
Alternatively, the flow sensing die and the IC die may be assembled
side-by-side. In both cases, the filler material may offer
protection to the IC die. The flow sensing die may be connected to
the IC die directly through bond wires or indirectly through
electrical connections through the substrate. The flow sensing die
may have through silicon vias (TSV), to avoid the presence of bond
wires and even further reduce the onset of unwanted turbulences.
Advantageously, a flow sensor with TSV can help with 3D stacking
techniques, whereby the flow sensing die sits on top of an IC (e.g.
ASIC), thus reducing the sensor system size.
[0101] Alternatively or additionally, circuital blocks may be
integrated on to the flow sensor itself. The membrane of the flow
sensor may occupy a small area of the flow sensing surface, leaving
a lot of area for monolithic integration of circuital blocks within
the flow sensing die. Circuitry may comprise IPTAT, VPTAT,
amplifiers, analogue to digital converters, digital to analogue
converters, memories, RF communication circuits, timing blocks,
filters or any other means for driving, readout, and electrical
signals manipulation and communication to the outside world. For
instance, in case of a thermal flow sensor, a heating element
driven in constant temperature mode results in enhanced performance
and having on-chip means to implement this driving method would
result in a significant advancement of the state-of-the-art flow
sensors. Also the driving method known a 3.omega. may be
implemented via on-chip means, or any other driving method, such as
constant temperature difference and time of flight, needed to
achieve specific performance (e.g. power dissipation, sensitivity,
dynamic response, range, fluid property detection).
[0102] The spacer may be monolithic with the lid.
[0103] The flow sensor assembly may further comprise a restrictor
located on the lid, and the second surface of the spacer may be in
contact with the restrictor.
[0104] The flow sensor may comprise: [0105] a sensor substrate
comprising an etched portion; [0106] a dielectric layer located on
the sensor substrate, wherein the dielectric layer comprises at
least one dielectric membrane located over the etched portion of
the sensor substrate; and [0107] a sensing element located on or
within the dielectric membrane.
[0108] The sensing element may comprise a metal layer located
within the dielectric membrane. The metal layer may comprise a
heater, a temperature sensor or other type of sensing element used
in a flow sensor.
[0109] The sensing element may comprise means to sense one or more
properties of the fluid (e.g. velocity, flow rate, exerted wall
shear stress, absolute pressure, differential pressure,
temperature, direction, thermal conductivity, diffusion
coefficient, density, specific heat, kinematic viscosity). The flow
sensor may be a thermal flow sensor, and said means to sense one or
more properties of the fluid may include heating elements and
temperature sensors. The flow sensor may be a mechanical flow
sensor, and said means to sense one or more properties of the fluid
may include piezo elements.
[0110] The starting substrate may be silicon, or silicon on
insulator (SOI). However, any other substrate combining silicon
with another semiconducting material compatible with
state-of-the-art CMOS fabrication processes may be used. Employment
of CMOS fabrication processes guarantees sensor manufacturability
in high volume, low cost, high reproducibility and wide
availability of foundries supporting the process. CMOS processes
also enable on-chip circuitry for sensor performance enhancement
and system integration facilitation.
[0111] The membrane or membranes may be formed by back-etching
using Deep Reactive Ion Etching (DRIE) of the substrate, which
results in vertical sidewalls and thus enabling a reduction in
sensor size and costs. However, the back-etching may also be done
by using anisotropic etching such as KOH (Potassium Hydroxide) or
TMAH (TetraMethyl Ammonium Hydroxide) which results in sloping
sidewalls. The membrane may also be formed by a front-side etch or
a combination of a front-side and back-side etch to result in a
suspended membrane structure, supported only by 2 or more beams.
The membrane may be circular, rectangular, or rectangular shaped
with rounded corners to reduce the stresses in the corners, but
other shapes are possible as well.
[0112] The dielectric membrane may comprise of silicon dioxide
and/or silicon nitride. The membrane may also comprise of one or
more layers of spin on glass, and a passivation layer over the one
or more dielectric layers. The employment of materials with low
thermal conductivity (e.g. dielectrics) enables a significant
reduction in power dissipation as well as an increase in the
temperature gradients within the membrane with direct benefits in
terms of sensor performance (e.g. sensitivity, frequency response,
range).
[0113] The dielectric region may comprise a dielectric layer or a
plurality of layers including at least one dielectric layer.
Generally speaking, a dielectric membrane region may be located
immediately adjacent to the etched portion of the substrate. The
dielectric membrane region corresponds to the area of the
dielectric region above (or below depending upon the configuration)
the etched cavity portion of the substrate. For example, in a
flip-chip configuration the dielectric membrane will be shown below
the etched cavity portion of the substrate. Each dielectric
membrane region may be over a single etched portion of the
semiconductor substrate.
[0114] The flow sensor may comprise a passivation layer located on
the dielectric layer.
[0115] A top surface of the passivation layer may be configured to
be non-planar. The top surface of the passivation layer may be
defined as the surface that is adjacent to the flow sensing channel
or the flow sensing surface. The top surface of the passivation
layer may comprise protrusions extending away from the dielectric
layer. The protrusions may comprise walls or ridges. Stacks may be
used within the dielectric layer to support the walls or
ridges.
[0116] Walls may be present on the flow sensing surface of the flow
sensing die. In case the filler material bleeds onto the flow
sensing surface of the flow sensing die, the walls act as barrier
for the filler material thus avoiding interaction of the filler
material with the flow sensing structure of the flow sensing
surface of the flow sensing die. The walls may be a by-product of a
non-planarised fabrication process. For example, metal structures
within a metal layer may be realised, resulting in a flow sensing
surface with extrusions following the pattern of the metal
structures within the metal layer. This effect may be further
enhanced if metal structures are realised within different metal
layers on top of each other.
[0117] A top surface of the passivation layer may comprise one or
more grooves. The grooves, trenches or recesses may be etched
portions of the passivation layer. These allow excess filler
material to extend or bleed into the grooves, for example when the
sensor assembly is heated in use. This reduces bleeding of the
filler material over the membrane.
[0118] Grooves or recesses may be present on the flow sensing
surface of the flow sensing die. In case the filler material bleeds
onto the flow sensing surface of the flow sensing die, the grooves
act as an accumulation volume for the filler material. This avoids
interaction of the filler material with the flow sensing structure
of the flow sensing surface of the flow sensing die.
[0119] The protrusions of the passivation layer may be used as an
alternative or in addition to the grooves within the passivation
layer. This reduces bleeding of the filler material onto the
dielectric membrane, which would reduce functionality of the flow
sensor.
[0120] The dielectric membrane may define a through-hole. The
through hole or aperture may extend through the membrane to allow
fluid to flow through the flow sensor.
[0121] To facilitate the assembly process and reduce failures
during soldering of the flow sensor assembly, the membrane may
comprise through holes (or membrane cavity vent holes). The vent
holes reduce any pressure increase within the membrane cavity that
may result in membrane breakages, damage or stress.
[0122] The flow sensor assembly may comprise a coating on surfaces
that are in contact with fluid flow through the device,
`flow.sub.se`. The coating may comprise a protective layer. The
coating can be engineered to provide the flow sensor assembly with
enhanced resilience to particles, humidity, condensation, corrosive
fluids and any other substance that can potentially affect the
performance or lifetime of the flow sensor assembly.
[0123] The flow sensor assembly may further comprise bond pads
located on an outer surface of the flow sensor assembly. The first
substrate may comprise additional bond pads, referred to as
internal bond pads. The flow sensor may comprise additional bond
pads, referred to as die bond pads. The outer surface of the flow
sensor assembly may be plastic, and the (outer) bond pads may be
made of metal. The outer bond pads may form an electrical
connection between the outer surface of the assembly and the
internal bond pads of the lead frame (first substrate). The
internal bond pads may form an electrical connection to the die
bond pads through bond wires.
[0124] The flow channel walls may be partly or fully covered and
protected by a protective layer. The protective layer may be a
conformal layer, thus following the topology of the flow channel
walls. The bond wires may also be conformally coated by the
protective layer. Anything else within the flow channel that in
absence of the protective layer would be in contact with the fluid
flow may also be conformally coated by the protective layer.
[0125] The entire flow sensor assembly (not only the flow channel
walls) may be coated by the conformal protective layer.
[0126] Alternatively, the protective layer may be deposited at
wafer level. In this case, only the flow sensing die would be
protected by the protective layer.
[0127] The protective layer may also be deposited during or at the
end of the assembly process. In these cases, only part of the flow
sensor assembly or the entire flow sensor assembly would be
protected by the protective layer.
[0128] The protective layer may protect fragile elements of the
flow sensor assembly from aggressive media (e.g. aggressive
liquids, corrosive gases, etc.) and also improve biocompatibility
of the flow sensor assembly for example in medical applications and
generally avoid direct interaction of some or all the elements
forming the flow sensor assembly with the fluid under test and/or
the environment.
[0129] The first substrate may define an aperture. The aperture of
the first substrate and the through-hole of the dielectric membrane
may form a hole through the flow sensor assembly. The aperture
reduces any pressure build up in the cavity underneath the
membrane, thus reducing the risk of failure during packaging of the
flow sensing die onto the substrate and during soldering of the
flow sensor assembly onto a second substrate (e.g. a PCB).
[0130] According to a further aspect of the disclosure, there is
provided a flow sensing system comprising: [0131] a main channel
extending in a first direction; [0132] a flow sensor assembly as
described above, wherein the flow sensor assembly is located in the
main channel such that the flow sensing channel of the flow sensor
assembly is substantially parallel to the main channel. The flow
sensor assembly may be located within a larger pipe or tube,
referred to as the main channel. The main channel may have a
substantially large cross sectional area than the flow sensing
channel. The flow sensor assembly may be disposed on a sidewall of
the larger pipe or tube.
[0133] In this setup, a portion of the flow going through the main
channel may also go through the flow sensor assembly.
[0134] The flow sensor assembly may be integrated on one side of a
main flow channel with a substantially greater cross-section area
than the first flow channel. The fluid flow going through this
second channel may be referred to as `Flow.sub.SY` and may have a
direction substantially parallel with `flow.sub.se`.
[0135] The flow sensor assembly may be located within the main flow
channel such that the flow sensing channel of the flow sensor
assembly is parallel with the main flow channel. The flow sensor
assembly may have openings corresponding to the open ends of the
flow inlet channel and the flow outlet channel located on two
opposite sides of the flow sensor assembly.
[0136] Alternatively, the flow sensor assembly may be rotated at an
angle less than 90.degree. with respect to the main flow channel,
more particularly, the flow sensor assembly may be rotated at angle
of 45.degree. with respect to the second main such that the flow
sensing channel extends in a direction non-parallel to the main
flow channel. The flow sensor assembly may have openings
corresponding to the open ends of the flow inlet channel and the
flow outlet channel, located on two adjacent sides of the flow
sensor assembly rather than on opposite sides.
[0137] According to a further aspect of the disclosure, there is
provided a method of manufacturing a flow sensor assembly, the
method comprising: [0138] forming a first substrate; [0139] forming
a flow sensor located over the first substrate; [0140] forming a
lid located over the first substrate and the flow sensor; [0141]
forming a flow inlet channel; [0142] forming a flow outlet channel;
[0143] forming an overmold laterally encircling the flow sensor and
in contact with the side walls of the flow sensor, wherein the
overmold extends between the flow sensor and the lid such that the
overmold, the flow sensor, and the lid define a flow sensing
channel between the flow inlet channel and the flow outlet channel,
and wherein the lid and the encapsulation cooperate to define the
flow inlet channel and the flow outlet channel.
[0144] According to a further aspect of the disclosure, there is
provided a method of manufacturing a flow sensing system, the
method comprising: [0145] providing a main channel extending in a
first direction; [0146] manufacturing a flow sensor assembly
according to the method as described above; [0147] positioning the
flow sensor assembly within the main channel such that the flow
sensing channel of the flow sensor assembly is substantially
parallel to the main channel.
BRIEF DESCRIPTION OF THE FIGURES
[0148] Some embodiments of the disclosure will now be described by
way of example only, and with reference to the accompanying
drawings, in which:
[0149] FIG. 1A shows schematically a cross-section of a flow sensor
assembly within a larger channel, according an embodiment of the
disclosure;
[0150] FIG. 1B shows an alternative cross-section of the flow
sensor assembly shown in FIG. 1A;
[0151] FIG. 1C shows a top view of the flow sensor assembly shown
in FIGS. 1A and 1B;
[0152] FIG. 2A shows schematically a cross-section of an
alternative flow sensor assembly having a restrictor in the
lid;
[0153] FIG. 2B shows an alternative cross-section of the flow
sensor assembly of FIG. 2A;
[0154] FIG. 3 shows schematically a cross-section of an alternative
flow sensor assembly having guide structures located on the
lid;
[0155] FIG. 4 shows schematically a cross-section of an alternative
flow sensor assembly having tapered inlet and outlet openings
formed by the lid and the encapsulation;
[0156] FIG. 5 shows schematically a cross-section of an alternative
flow sensor assembly having a recess in the lid;
[0157] FIG. 6 shows schematically a cross-section of an alternative
flow sensor assembly having a protrusion formed on the
encapsulation;
[0158] FIG. 7 shows schematically a cross-section of an alternative
flow sensor assembly having a protrusion on the encapsulation and a
restrictor feature on the lid;
[0159] FIG. 8 shows schematically a cross-section of an alternative
flow sensor assembly having additional side channels;
[0160] FIG. 9 shows schematically a top view of an alternative flow
sensor assembly having a by-pass channel within the package;
[0161] FIG. 10 shows schematically a top view of an alternative
flow sensor assembly having a by-pass channel within the package,
and restrictors and fins within the flow path;
[0162] FIG. 11A shows schematically a cross-section of an
alternative flow sensor assembly having an out-of-plane by-pass
channel;
[0163] FIG. 11B shows schematically another cross-section of a flow
sensor assembly having an out-of-plane by-pass channel;
[0164] FIG. 12 shows schematically a cross-section of an
alternative flow sensor assembly having a protective coating within
the flow channel;
[0165] FIG. 13 shows schematically a cross-section of an
alternative flow sensor assembly having vertical alignment
structures;
[0166] FIG. 14 shows a top view of the flow sensor assembly shown
in FIG. 13;
[0167] FIG. 15 shows schematically a cross-section of an
alternative flow sensor assembly with alignment structures that
operate as a flow guide;
[0168] FIG. 16 shows a top view of the flow sensor assembly shown
in FIG. 15;
[0169] FIG. 17 shows schematically a top view of a flow sensor
assembly having horizontal alignment structures;
[0170] FIG. 18 shows a cross-section of the flow sensor assembly
shown in FIG. 17;
[0171] FIG. 19 shows schematically a top view of an alternative
flow sensor assembly having horizontal alignment structures;
[0172] FIG. 20 shows a cross-section of the flow sensor assembly
shown in FIG. 19;
[0173] FIG. 21 shows schematically a top view of an alternative
flow sensor assembly having horizontal alignment structures;
[0174] FIG. 22 shows a cross-section of the flow sensor assembly
shown in FIG. 21;
[0175] FIG. 23 shows schematically a top view of an alternative
flow sensor assembly having horizontal alignment structures;
[0176] FIG. 24 shows a cross-section of the flow sensor assembly
shown in FIG. 23;
[0177] FIG. 25A shows schematically a top view of a flow sensor
assembly;
[0178] FIG. 25B shows a cross-section of the flow sensor assembly
shown in FIG. 25A; FIG. 25C shows an alternative cross-section of
the flow sensor assembly shown in FIGS. 25A and 25B;
[0179] FIG. 26 shows schematically a cross-section of an
alternative flow sensor assembly having the inlet and outlet each
comprising a restrictor and the flow sensing die stacked on top of
the ASIC;
[0180] FIG. 27 shows schematically a cross-section of an
alternative flow sensor assembly having the flow sensing die
arranged side by side with the ASIC;
[0181] FIG. 28 shows schematically a cross-section of an
alternative flow sensor assembly having the inlet and outlet
located above the flow sensing die;
[0182] FIG. 29 shows schematically a cross-section of an
alternative flow sensor assembly having the inlet and outlet
arranged parallel to the flow channel;
[0183] FIG. 30 shows schematically a cross-section of an
alternative flow sensor assembly having the inlet and outlet
arranged parallel to the flow;
[0184] FIG. 31 shows schematically a cross-section of an
alternative flow sensor assembly having filler material protecting
the bond wires;
[0185] FIG. 32 shows schematically a cross section of a flow
sensing die having grooves on the flow sensing die surface;
[0186] FIG. 33 shows schematically a cross section of a flow
sensing die having walls on the flow sensing die surface;
[0187] FIG. 34A shows schematically a cross-section of an
alternative flow sensor assembly having recesses on the lid to
receive adhesive;
[0188] FIG. 34B shows schematically a cross section of a flow
sensing assembly having recesses on the lid to receive adhesive and
with excess lid attach present; and
[0189] FIG. 34C shows schematically a cross section of a flow
sensing assembly having recesses on the lid to receive adhesive,
with excess lid attach present along, and having an epoxy recess
link.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0190] FIGS. 1A to 1C show a flow sensor assembly according to the
disclosure. FIG. 1C shows a top view of the flow sensor assembly,
FIG. 1A shows a cross-section of the device of FIG. 1C taken along
the line A-A', and FIG. 1B shows a cross-section of the device of
FIG. 1C taken along the line B-B'.
[0191] The flow sensor assembly includes a flow sensor 1 comprising
a flow sensing area 3 above a substrate 10. Bond wires 4 form an
electrical connection between the flow sensor 1 and the substrate
10. An encapsulation or overmold 200 covers part of the flow sensor
1 and substrate 10, and also covers the bond wires 4, but leaves
the flow sensing area 3 exposed. A lid 6 is placed above the
encapsulation such that the lid is in contact with the top surface
of the encapsulation 302.
[0192] The top surface of the flow sensor 1, the encapsulation 200
and the lid 6 together define a flow sensing channel through the
flow sensor assembly. The encapsulation 200 is deposited such that
it is level with a top surface of the flow sensor 1 in central
region parallel to the direction of flow to form a lower surface
306 of the flow sensing channel. The encapsulation 200 forms sloped
sidewalls 304 of the flow sensing channel.
[0193] The flow sensor assembly has first and second sides
perpendicular to the top surface of the flow sensor 1, where the
first and second sides have one opening between the lid 6 and the
encapsulation 200, or between the substrate 10 and the lid 6, and
the flow sensing channel between these two openings. The flow
sensor assembly is placed in a much bigger flow path 201, for
example the larger flow path 201 may be a larger channel or pipe.
The flow sensor assembly is on an interior surface of the larger
channel 201 and is placed such that the flow sensing channel
through the flow sensor assembly is parallel to the direction of
flow, Flow.sub.SY, through the larger channel 201. Flow through the
sensor assembly, flow.sub.se, can enter the flow sensor assembly,
travel through the flow sensor assembly, and leave the flow sensor
assembly with minimal disturbance.
[0194] The fluid flow going through the first flow channel is
referred to as `flow.sub.se` and has a direction substantially
parallel with the flow sensor top surface as indicated by the
dotted circle symbol. The flow sensor assembly is integrated on one
side of a main flow channel with a substantially greater
cross-section area than the first flow channel. The fluid flow
going through this second channel may be referred to as
`Flow.sub.SY` and may have a direction substantially parallel with
`flow.sub.se` as indicated by the dotted circle symbol.
[0195] FIG. 2A shows a cross-section of a cross-section of an
alternative flow sensor assembly having a restrictor 202 in the lid
(taken along the line A-A' shown in FIG. 1C), and FIG. 1B shows a
cross-section of the device of FIG. 2A taken along the line
B-B'.
[0196] The flow sensor assembly of FIG. 2 is similar to that shown
in FIG. 1, however there is a restrictor 202 on the lid 6. The
restrictor 202 is located above the flow sensing surface 3 of the
flow sensor 1, thereby narrowing the flow sensing channel above the
flow sensor 1. This helps to improve the flow above the flow
sensing area 3, and hence the sensitivity of the device.
[0197] FIG. 3 shows a cross-section of an alternative flow sensor
assembly having guide structures 203 located on the lid 6, and
directly above the flow sensing surface 3 of the flow sensor. The
guide structures 203 extend in the direction of flow, flow.sub.se,
through the flow sensor assembly. The guide structure 203 improve
the flow within the flow sensing channel and thus improve the
sensitivity of the flow sensor assembly.
[0198] FIG. 4 shows schematically a cross-section of an alternative
flow sensor assembly having tapered inlet and outlet openings
formed by the lid 6 and the encapsulation 200. As such, the flow
inlet channel and the flow outlet channel of the flow sensor
assembly have a larger cross-sectional area at the sides of the
flow sensor assembly, than the cross-sectional area of the flow
sensing channel through the device. The tapered inlet and outlet
openings allow a larger portion of the main flow within a larger
flow channel in which the flow sensor assembly is located, to go
through the flow sensor assembly. This improves the sensitivity of
the flow sensor assembly. In this example, both the lid 6 and the
encapsulation 200 have a greater thickness towards the centre of
the device to form the tapered openings, however only the lid 6 or
the encapsulation 200 may have a greater thickness towards the
centre of the device.
[0199] FIG. 5 shows a cross-section of an alternative flow sensor
assembly having a recess 212 in the lid. In this example, the
sidewalls of the recess 212 are aligned with the sidewalls of the
flow sensing channel formed by the overmold 200, such that the
cross-sectional area of the flow sensing channel is increased. The
recess 212 increases the amount of fluid flowing through the flow
path.
[0200] FIG. 6 shows schematically a cross-section of an alternative
flow sensor assembly having a protrusion 204 located on the
encapsulation 200. The protrusions 204 may be monolithic with the
overmold 200. In this example, the protrusions are laterally spaced
from the flow sensor to cause a flow velocity increase close to the
protrusions, whilst allowing the flow velocity to reduce towards
its original value before reaching the flow sensor. The protrusions
improve the flow conditioning before it reaches the flow sensing
channel.
[0201] FIG. 7 shows schematically a cross-section of an alternative
flow sensor assembly having a protrusion 204 on the encapsulation
and a restrictor 202 on the lid. The restrictor 202 is similar to
that shown in FIG. 2, and the protrusions 204 are similar to those
shown in FIG. 6. The protrusion may also be referred to as a bump.
The bump can be located anywhere inside the flow sensing channel
outside of the flow sensing area, and there can be one or more
bumps. The restrictor 202 in the lid 6 can be preferably above the
flow sensing area, but can also be in other regions along the path,
and there can be more than one restrictor. The restrictor 202 and
bumps 204 can also be tapered as shown in the figure, or can be
square or curved shape.
[0202] FIG. 8 shows schematically a cross-section of an alternative
flow sensor assembly having additional side channels 205. In this
example, the additional side channel 205 may or may not be
connected to the flow sensing channel. The additional side channels
205 prevent unwanted turbulences within the flow, flow.sub.se,
within the flow sensing channel.
[0203] FIG. 9 shows a top view of an alternative flow sensor
assembly having a by-pass channel 207 within the package. In the
embodiments shown in FIGS. 9 and 10 there is one main channel 206
through the flow sensor assembly, and one by-pass flow path 207
forming the flow sensing channel. The main channel 206 and the
by-pass channel 207 are located within the same plane. The main
channel 206 and the by-pass channel 207 are both connected to the
same flow inlet channel and the same flow outlet channel, and the
by-pass flow path 207 is connected to and parallel to the main
channel 206. The flow sensor 1 is placed within the by-pass flow
path 207. The flow travelling through the flow sensing channel,
flow.sub.se, is a portion of the total flow entering the flow
sensor assembly, flow.sub.SE. In this way, the flow sensor is not
exposed to the larger flow, flow.sub.SE, and is only exposed to the
smaller flow, flow.sub.se. This is useful when the flow rate,
flow.sub.SE, in the main channel 206 is very high. It also protects
the flow sensor against dust particles that may be present in the
main channel 206, but are less likely to be present in the by-pass
flow path 207.
[0204] The flow sensor assembly of FIG. 10 is similar to that shown
in FIG. 9. In the embodiment shown in FIG. 10, there are fins 208
present in the main flow path. There is also a restriction feature
209 present. Both of these features help to improve the fluid flow
through the flow paths. The restriction 209 reduces the chances of
particles in flow from reaching the flow sensing channel. The fins
208 are horizontal partition in the direction of flow and help to
make the flow laminar. Further elements such as guide structures,
pressure drop elements, or additional openings may also be
present.
[0205] FIG. 11 shows schematically a cross-section of an
alternative flow sensor assembly having with an out-of-plane
by-pass channel;
[0206] FIG. 11A and 11B show another example of a flow sensor
assembly where there is a main flow channel 210 and a bypass flow
path forming the flow sensing channel. Similar to FIGS. 9 and 10,
the main flow channel 210 and flow sensing channel are both
connected to the same flow inlet channel and the same flow outlet
channel, and the by-pass flow path is connected to and parallel to
the main channel 210. The flow sensor 1 is located within the
bypass channel. In this embodiment, the main flow channel 210 and
by-pass flow path are separated vertically. In the embodiment
shown, the main flow channel 210 is located within the lid 6.
[0207] The main channel 210 has a larger cross sectional area than
the flow sensing channel.
[0208] As such, similar to the embodiment shown in FIGS. 9 and 10,
the flow travelling through the flow sensing channel, flow.sub.se,
is smaller than the flow travelling through the main channel 210,
flow.sub.SE. In this way, the flow sensor is not exposed to the
larger flow, flow.sub.SE, and is only exposed to the smaller flow,
flow.sub.se.
[0209] FIG. 12 shows a cross-section of an alternative flow sensor
assembly having a protective coating 211 within the flow channel.
In this embodiment, the protecting coating 211 is located over the
lower surface of the lid, the upper surface of the encapsulation
200 and the upper surface of the flow sensor 1 that together define
the flow sensing channel. The coating protects the sensor against
corrosive fluids.
[0210] FIG. 13 shows a cross-section of an alternative flow sensor
assembly having vertical alignment structures, and FIG. 14 shows a
top view of the flow sensor assembly shown in FIG. 13. In the
embodiment of FIG. 13 and FIG. 14, there are alignment structures
on the lid 6 that define the vertical distance between the lid 6
and the flow sensor 1, thereby defining the height of the flow
sensing channel. The alignment structures may also be referred to
as spacers.
[0211] A flow sensor chip 1 is attached to a substrate 10 by means
of a die attach 103. A lid 6 is attached to the substrate by means
of a lid attach 104. In this embodiment, the die attach 103 and the
lid attach 104 may be an adhesive joining the flow sensor 1 and the
substrate 10 and the lid 6 and the substrate 10 respectively.
However, the die attach 103 and the lid attach 104 may be another
fixing means. The lid 6 has vertical alignment structures 100 to
allow better alignment of the lid with the flow sensor chip 1. By
contacting the top of the sensor chip 1, the effect of tolerances
in the lid attach 103 thickness and the die attach 104 thickness
can be reduced or eliminated. The alignment structure 100 may limit
the minimum height of the flow channel (in situations where the
alignment structures 100 do not contact the top of the flow sensor
1), and may define the exact height of the flow sensing channel (in
situations where the alignment structures 100 do contact the top of
the flow sensor 1).
[0212] In this embodiment, the alignment structures 100 are shown
as 4 cylindrical supports located in line with the corners of the
flow sensor 1 to reduce the effect of the alignment structures 100
on flow within the flow sensing channel. However, there may be more
or less alignment structures and they may be aligned with different
regions of the flow sensor 1.
[0213] FIG. 15 shows a cross-section of an alternative flow sensor
assembly with alignment structures 101 that operate as a flow
guide, and FIG. 16 shows a top view of the flow sensor assembly
shown in FIG. 15. The alignment structures 101 of FIGS. 15 and 16
are similar to those shown in FIG. 13, however in this embodiment
they are provided as two structures extending laterally through the
flow sensor assembly parallel to two opposite edges of the flow
sensor 1.
[0214] FIG. 15 and FIG. 16 illustrate how a single set of features
101 could define both the vertical alignment between the flow
sensor 1, the lid 6, and the substrate 10, and also can further
define sidewalls of the flow sensing channel through the flow
sensor assembly and over the sensor chip 1. In this embodiment, the
alignment structures 101 are aligned with an area of the flow
sensor 1 in between the two sets of bond wires 4, so that the bond
wires 4 are located outside the alignment structures 101 and the
sidewalls of the flow sensing channel. The alignment structures 101
act as flow guides.
[0215] FIG. 17 shows a top view of a flow sensor assembly having
horizontal alignment structures 102, and FIG. 18 shows a
cross-section of the flow sensor assembly shown in FIG. 17. FIG. 17
and FIG. 18 illustrate how lid alignment features 102 could be used
to define the vertical alignment between the flow sensor 1, the lid
6, and the substrate 10, and the horizontal alignment between the
lid 6 and the sensor chip 1. As shown in FIG. 17, the alignment
structures 102 overlap with the flow sensor 1 and an area outside
the flow sensor. A lower, inner corner of each alignment structure
102 overlapping with a respective corner of the flow sensor 1 is
chamfered, as shown when viewed from the side in FIG. 18, so that
both horizontal and vertical alignment is achieved automatically as
the lid 6 is lowered onto the sensor chip 1 and package substrate
6.
[0216] FIG. 19 shows a top view of an alternative flow sensor
assembly having horizontal alignment structures, and FIG. 20 shows
a cross-section of the flow sensor assembly shown in FIG. 19. In
this embodiment, the alignment structures 102 are supports having
an L shape when viewed from the top and are aligned around each
corner of the flow sensor 1 so that each corner of the flow sensor
1 is surrounded by an alignment structure 102. In this embodiment,
there are four structures 102--one aligned with each corner of the
flow sensor 102. However, there may be less than four alignment
structures.
[0217] FIG. 21 shows a top view of an alternative flow sensor
assembly having horizontal alignment structures, and FIG. 22 shows
a cross-section of the flow sensor assembly shown in FIG. 21. In
this embodiment, the alignment structures 102 are flat structures
and aligned with and laterally spaced from the side edges of the
flow sensor 1. In this embodiment, four structures 102 are
shown--one aligned with each edge of the flow sensor. However,
there may be less than four alignment structures. The alignment
structures 102 that are aligned with the sides of the flow sensor 1
having bond wires 4 are located between the bond wires 4.
[0218] It should be noted that in FIGS. 19-22, the alignment
structures can be either in direct contact with the flow sensing
die, or can be located within 50 .mu.m from the flow sensing die.
Providing the alignment structures within 50 .mu.m of the flow
sensing die provides alignment whilst also allowing for
manufacturing tolerances of the alignment structures and the flow
sensing die. One or more surfaces of the alignment structures or
spacers, for example the lower surface or a side surface of an
alignment structure, may be located within 50 .mu.m of one of the
surfaces, for example the top surface or a side surface, of the
flow sensor die.
[0219] FIG. 23 shows schematically a top view of an alternative
flow sensor assembly having horizontal alignment structures, and
FIG. 24 shows a cross-section of the flow sensor assembly shown in
FIG. 23. In this embodiment, the alignment structures 102 are and
aligned with and overlap the side edges of the flow sensor 1. A
lower, inner corner of each alignment structure 102 overlapping
with a respective corner of the flow sensor 1 is chamfered.
[0220] FIG. 25A shows schematically a top view of a flow sensor
assembly;
[0221] FIG. 25B shows a cross-section of the flow sensor assembly
shown in FIG. 25A;
[0222] FIG. 25B shows an alternative cross-section of the flow
sensor assembly shown in FIGS. 25A and 25B;
[0223] FIG. 25A shows a top view of a flow sensor assembly
according to an embodiment of the disclosure. The flow sensor
assembly includes flow sensing die or flow sensor 1, having a flow
sensing surface 3, comprising a membrane 2. The flow sensing die 1
is electrically connected to the substrate (first substrate) with
bond wires 4. The substrate comprises a rim 5. The flow sensor
assembly also comprises a lid 6, comprising an inlet or flow inlet
channel 7 and an outlet or flow outlet channel 8, both comprising
hoses 9. Alignment structures 100 (not shown in FIG. 25A) improve
the vertical alignment of the lid with respect to the flow
sensor.
[0224] FIG. 25B shows a schematic cross section of the flow sensor
assembly of FIG. 25A along the cut line A-A', and FIG. 25C shows a
schematic cross section of the flow sensor assembly of FIG. 25A
along the cut line B-B'. The gap between the rim 5 and the flow
sensing die 1 is filled with a filler material 11 with a convex
surface topology. As can be seen in FIG. 25B, both the inlet 7 and
an outlet 8 have hoses 9.
[0225] For connection, the flow sensor assembly has outer bond pads
located on an outer surface of the flow sensor assembly. The
substrate 10 also has bond pads, referred to as internal bond pads,
and the flow sensor may comprise additional bond pads on the
dielectric membrane, referred to as die bond pads. The outer 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
through the bond wires.
[0226] In the embodiment shown in FIGS. 25A, 25B, and 25C, the flow
sensing die is assembled onto a substrate (e.g. a lead frame, a
printed circuit board, or any other substrate mechanically
supporting the die and offering an electrical connection from the
die to the outside world). The substrate comprises a rim. The rim
may be integral part of the substrate, integral part of the lid or
an additional element assembled onto the substrate as part of the
flow sensor assembly process. As a result, a cavity between the rim
and the flow sensing die is formed. To reduce turbulences in
proximity to the flow sensing surface of the flow sensing die the
cavity is filled with a filler material. Depending on the filler
deposition method, the surface topology of the filler may be
concave or convex. The filler material also protects the substrate
bond pads and offers partial protection to the bond wires.
[0227] The flow sensor assembly also has a lid with a flow inlet
and a flow outlet both comprising hoses to facilitate mechanical
connection to the system using it. Hoses may have any geometry that
facilitate mechanical connection to the system using the flow
sensor assembly. For instance, the hoses may have barbs, grooves,
protrusions or a combination of those to enhance friction with the
pipes or any other mean connected to them. The number, size and
position within the flow sensor assembly of the inlet and the
outlet might vary depending on the application requirements.
[0228] FIG. 26 shows a cross-section of an alternative flow sensor
assembly having the inlet and outlet each comprising a restrictor
and the flow sensing die stacked on top of the ASIC. This
embodiment is similar to that shown in FIG. 25, however in this
embodiment, the gap between the rim 5 and the flow sensing die 1 is
filled with a filler material 11 with a concave surface topology.
The flow sensor assembly also comprises a lid 6, comprising an
inlet 7 and an outlet 8, both comprising hoses 9 and channel
restrictors 13.
[0229] A non-uniform flow channel cross-sectional area is achieved
by the use of restrictors (i.e. the flow channel cross-sectional
area is locally reduced). Restrictors are placed at the flow inlet
and flow outlet to reduce the effect on the flow sensing
performance of the flow sensor assembly when integrated into the
system using it.
[0230] The protrusions or hoses are substantially perpendicular to
the flow sensing channel, and the flow inlet channel and flow
outlet channel may then be substantially perpendicular to the
sensing channel. In this embodiment, fluid enters and exits the
flow sensor in opposite directions.
[0231] The flow sensing die is stacked on top of the IC die to
reduce the overall flow sensor assembly form factor. Alternatively,
the flow sensing die and the IC die may be assembled side-by-side,
as shown in FIG. 27. In both cases, the filler material offers
protection to the IC die.
[0232] FIG. 27 shows a cross-section of an alternative flow sensor
assembly having the flow sensing die laterally adjacent to the
ASIC. This embodiment is similar to those shown in FIGS. 25 and 26,
however in this embodiment, 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 with bond wires 4. The IC is electrically
connected to substrate 10. The gap between the rim 5 and the flow
sensing die 1 is filled with a filler material 11 fully covering
the IC 12.
[0233] FIG. 28 shows a cross-section of an alternative flow sensor
assembly having the inlet and outlet located above the flow sensing
die and terminating on the top surface of the lid. This embodiment
is similar to those shown in FIGS. 25 to 27, however in this
embodiment, the inlet 7 and outlet 8 are both located over the flow
sensor 1, which has an integral extension portion to reduce
turbulence. The flow sensing die 1 comprises a flow sensing area 3
extending underneath both the inlet 7 and the outlet 8.
[0234] In FIGS. 25A to 28, the surface within or around the flow
sensor may have a first region underneath the channel inlet 7, and
a second region underneath the channel outlet 8, where the surface
between the first and second region is substantially flat.
[0235] FIG. 29 shows a cross-section of an alternative flow sensor
assembly having the inlet and outlet arranged parallel to the flow
channel. In this embodiment, the flow inlet channel 7 and the flow
outlet channel 8 are defined as the space between the lid 6 and the
rim 5. The flow sensor assembly includes a lid restrictor 13.
[0236] The lid comprises a restrictor, placed along the flow
channel in proximity of the flow sensing surface of the flow
sensing die to locally increase the flow speed and thus improve the
flow sensing performance. Upon assembly of the lid on the rim of
the substrate a flow inlet, a flow outlet, and flow channel are
created. The flow sensor assembly described in this embodiment is
suitable in applications where the flow sensor assembly is soldered
on a surface over which a fluid is flowing, and the application
requires measuring a property of the flowing fluid.
[0237] FIG. 30 shows a cross-section of an alternative flow sensor
assembly having the inlet and outlet arranged parallel to the flow.
In this embodiment, the device has a lid restrictor 13, and the
flow sensor 1 has an extension portion.
[0238] In FIGS. 29 and 30, the flow channel surface around the flow
sensor, and in the entire region below the restrictor 13 is
substantially flat. The two ends of the restrictor 13 act as a
guide for the fluid into the flow sensing channel directly above
the flow sensor, and so are the input and output points of the flow
sensing channel, and the surface below them is substantially
flat.
[0239] FIG. 31 shows a cross-section of an alternative flow sensor
assembly having filler material completely encapsulating and
protecting the bond wires. In this embodiment, the gap between the
rim 5 and the flow sensing die 1 is filled with a filler material
11 completely covering the bond wires 4. To reduce turbulences in
proximity of the flow sensing surface of the flow sensing die the
cavity between the rim 5 and the flow sensor 1 is filled with a
filler material 11. Due to surface tension effects, the filler
material 11 fully encapsulates the bond wires and the die bond PADs
for extra protection. The lid is assembled on the rim of the
substrate.
[0240] In FIGS. 25B to 31 the alignment structures shown are for
vertical alignment. However, other alignment structures such as
those shown in FIGS. 13 to 24 may also be used. The alignment
structures may also be used for horizontal alignment, or for both
horizontal and vertical alignment. The alignment structures can
also be used as flow guides.
[0241] Furthermore, other types of package design, such as chip
scale packages, or packages with through silicon vias or flip chip
that don't require wire bonds are also possible.
[0242] Further, the structures can also be for alignment to the
first substrate rather than the flow sensor chip.
[0243] FIG. 32 shows schematically a cross section of a flow
sensing die having grooves on the flow sensing die surface. The
flow sensing die 1 may be used in any of the flow sensor assemblies
shown in FIGS. 1 to 31. The flow sensor 1 comprises a flow sensing
surface 3, comprising a membrane 2. The flow sensing die 1 also
comprises a passivation layer 14, a metal layer 15 acting as a
sensing element embedded within a dielectric layer 16 and a die
substrate 17 partly etched through to realise the membrane 2. The
passivation layer 14 is also partly etch through to realise grooves
18 on the flow sensing surface 2. The membrane also comprises a
through-hole 19.
[0244] In this embodiment, grooves are present on the flow sensing
surface of the flow sensing die. In case the filler material bleeds
onto the flow sensing surface of the flow sensing die, the grooves
act as an accumulation volume for the filler material. This avoids
interaction of the filler material with the flow sensing structure
of the flow sensing surface of the flow sensing die.
[0245] FIG. 33 shows a cross section of a flow sensing die having
walls on the flow sensing die surface. The flow sensor 1 comprises
a flow sensing surface 2, comprising a membrane 3. The flow sensing
die 1 also comprises a passivation layer 14, a metal layer 15
embedded within a dielectric layer 16 and a die substrate 17 partly
etched through to realise the membrane 3. The passivation layer 14
is also made non-planar by mean of metal stacks 20 to realise walls
21 on the flow sensing surface 2.
[0246] In this embodiment, walls are present on the flow sensing
surface of the flow sensing die. In case the filler material bleeds
onto the flow sensing surface of the flow sensing die, the walls
act as barrier for the filler material thus avoiding interaction of
the filler material with the flow sensing structure of the flow
sensing surface of the flow sensing die. The walls may be a
by-product of a non-planarised fabrication process. For example,
metal structures within a metal layer may be realised, resulting in
a flow sensing surface with extrusions following the pattern of the
metal structures within the metal layer. This effect may be further
enhanced if metal structures are realised within different metal
layers on top of each other.
[0247] It should be noted that while FIGS. 32 and 33 show a flow
sensing die with grooves, through-holes and walls, a flow sensing
die without these features can also be used for the sensor
assemblies shown in FIGS. 1-31.
[0248] FIG. 34A shows schematically a cross-section of a flow
sensor assembly having recesses on the lid to receive adhesive, and
FIG. 34B shows a cross section of a flow sensing assembly with
excess adhesive present.
[0249] FIG. 34A illustrates a flow sensor assembly where the lid 6
has recesses 110. These recesses allow some of the lid attach 104
to escape into the recesses 110. In this way excess lid attach goes
into the recesses rather than the flow channel. This improves the
reproducibility of the devices and gives a better process window
for fabrication.
[0250] FIG. 34B illustrates the effect of the epoxy recesses 110
when there is excess lid attach. On the left side of the lid there
are no recesses, so the lid attach seeps out as excess epoxy 111
into the flow channel. On the right side there are recesses 110,
and the excess epoxy 111 escapes into the recesses rather than into
the flow channel.
[0251] FIG. 34C illustrates the use of an epoxy recess link 112. On
a first side of the flow sensor assembly, shown as the left side in
this example, there are no links, so while the lid attach seeps out
as excess epoxy 111 in the epoxy recess 110, there is also air
trapped in the epoxy recess 110. At high ambient temperatures, or
with temperature cycling, pressure can build up inside this cavity,
which can cause damage to the lid 6. A solution to this is shown in
the right side of the figure where there is a gap or aperture
through the sidewall of the epoxy recess 110 in the lid, fluidly
connecting the epoxy recess 110 with the flow sensing channel. The
gaps may be referred to as epoxy recess links 112. The epoxy recess
links 112 may be substantially smaller than the epoxy recesses 110.
The epoxy recess links 112 allow air to escape from the epoxy
recess 110 and prevent build-up of pressure within the epoxy recess
110.
[0252] The skilled person will understand that in the preceding
description and appended claims, positional terms such as `above`,
`overlap`, `under`, `lateral`, etc. are made with reference to
conceptual illustrations of a device, such as those showing
standard cross-sectional perspectives and those shown in the
appended drawings. These terms are used for ease of reference but
are not intended to be of limiting nature. These terms are
therefore to be understood as referring to a device when in an
orientation as shown in the accompanying drawings.
[0253] Although the invention has been described in terms of
preferred embodiments as set forth above, it should be understood
that these embodiments are illustrative only and that the claims
are not limited to those embodiments. Those skilled in the art will
be able to make modifications and alternatives in view of the
disclosure, which are contemplated as falling within the scope of
the appended claims. Each feature disclosed or illustrated in the
present specification may be incorporated in the disclosure,
whether alone or in any appropriate combination with any other
feature disclosed or illustrated herein.
[0254] Many other effective alternatives will occur to the person
skilled in the art. It will be understood the disclosure is not
limited to the described embodiments, but encompasses all the
modifications that fall within the spirit and scope of the
disclosure.
TABLE-US-00001 Reference Numerals 1 Flow sensor 2 Dielectric
membrane 3 Flow sensing area 4 Bond wires 5 Rim 6 Lid 7 Flow inlet
channel 8 Flow outlet channel 9 Hose 10 Substrate 11 Filler
material 12 Integrated Circuit 13 Channel Restrictor 14 Passivation
Layer 15 Metal Layer 16 Dielectric Layer 17 Die Substrate 18 Groove
19 Membrane through-hole 20 Metal Stack 21 Walls 100 Alignment
structure 101 Alignment structure - flow guide 102 Horizontal
Alignment Structure 103 Die attach 104 Lid attach 110 Recess 111
Excess adhesive 112 Epoxy Recess Link 200 Encapsulation 201 Flow
sensing system channel 202 Restrictor 203 Guide structure 204
Protrusion 205 Additional Flow Path 206 Main Flow Path 207 By-pass
Flow Path 208 Fin 209 Restrictor 210 Main channel 211 Protective
Coating 212 Lid recess 302 Lid-encapsulation surface 304 Flow
sensing channel side-wall 306 Flow sensing channel lower wall
* * * * *