U.S. patent application number 12/782325 was filed with the patent office on 2011-11-24 for modular pressure sensor.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. Invention is credited to Gregory C. Brown, Thomas A. Larson, Curtis Rahn.
Application Number | 20110283802 12/782325 |
Document ID | / |
Family ID | 44645301 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110283802 |
Kind Code |
A1 |
Brown; Gregory C. ; et
al. |
November 24, 2011 |
MODULAR PRESSURE SENSOR
Abstract
A pressure sensor device for a modular pressure sensor package
is provided, comprising a substrate having a pressure port that
extends through the substrate from a first side of the substrate to
a second side of the substrate. A pressure sensor die is attached
to the first side of the substrate, forming a seal over the
pressure port on the first side of the substrate. A cover is
attached to the first side of the substrate over the pressure
sensor die, forming a sealed cavity wherein the pressure sensor die
is located within the cavity. The device also comprises a plurality
of electrical connectors mounted to the substrate external to the
cavity, the plurality of electrical connectors electrically coupled
to the pressure sensor die. Further, the substrate includes at
least one mounting element configured to secure a pressure port
interface to the second side of the substrate in a position around
the pressure port.
Inventors: |
Brown; Gregory C.;
(Chanhassen, MN) ; Larson; Thomas A.; (St. Louis
Park, MN) ; Rahn; Curtis; (Plymouth, MN) |
Assignee: |
HONEYWELL INTERNATIONAL
INC.
Morristown
NJ
|
Family ID: |
44645301 |
Appl. No.: |
12/782325 |
Filed: |
May 18, 2010 |
Current U.S.
Class: |
73/706 |
Current CPC
Class: |
G01L 19/003
20130101 |
Class at
Publication: |
73/706 |
International
Class: |
G01L 7/00 20060101
G01L007/00 |
Claims
1. A pressure sensor device for a modular pressure sensor package,
the pressure sensor device comprising: a substrate having a
pressure port that extends through the substrate from a first side
of the substrate to a second side of the substrate; a pressure
sensor die attached to the first side of the substrate, forming a
seal over the pressure port on the first side of the substrate; a
cover attached to the first side of the substrate over the pressure
sensor die, forming a sealed cavity wherein the pressure sensor die
is located within the cavity; and a plurality of electrical
connectors mounted to the substrate external to the cavity, the
plurality of electrical connectors electrically coupled to the
pressure sensor die; wherein the substrate includes at least one
mounting element configured to secure a pressure port interface to
the second side of the substrate in a position around the pressure
port.
2. The pressure sensor device of claim 1, further comprising: a
plurality of wire bonding pads located within the cavity, wherein
the pressure sensor die is electrically connected to the plurality
of wire bonding pads by a plurality of wire bonds; and wherein the
substrate further comprises a plurality of wire traces that
electrically connect the plurality of wire bonding pads to the
plurality of electrical connectors.
3. The pressure sensor device of claim 1, wherein the plurality of
electrical connectors are mounted onto the first side of the
substrate.
4. The pressure sensor device of claim 1, wherein the substrate
comprises a low temperature co-fired ceramic, a high temperature
co-fired ceramic, or a combination thereof.
5. The pressure sensor device of claim 1, wherein the substrate
comprises at least one stress isolation trench proximate to the
pressure sensor die and within the cavity.
6. The pressure sensor device of claim 1, further comprising the
pressure port interface mounted to the substrate.
7. The pressure sensor device of claim 1, wherein the at least one
mounting element comprises one of through holes or fold over tabs
for mounting the pressure port interface to the substrate.
8. The pressure sensor device of claim 1, further comprising at
least one integrated circuit device, transistor, or capacitor
mounted to the substrate within the cavity.
9. The pressure sensor device of claim 1, wherein the cover
comprises silicon and is thermoelectric bonded to the
substrate.
10. The pressure sensor device of claim 1, wherein the cover is
brazed to the ceramic substrate.
11. A modular pressure sensor, comprising: a pressure sensor
device, including a substrate having a pressure port that extends
through the substrate from a first side of the substrate to a
second side of the substrate; a pressure sensor die bonded to the
first side of the substrate, forming a seal over the pressure port
on the first side of the substrate; a cover bonded to the first
side of the substrate over the pressure sensor die, forming a
sealed cavity wherein the pressure sensor die is located within the
sealed cavity; and a plurality of electrical connectors mounted to
the substrate external to the cavity, the plurality of electrical
connectors electrically coupled to the pressure sensor die; and a
pressure port interface secured to the second side of the
substrate, the pressure port interface including: a cavity that
extends through the pressure port interface from a first side of
the pressure port interface to a second side of the pressure port
interface; wherein the pressure port of the substrate is aligned to
and in communication with the cavity of the pressure port interface
at the first side of the pressure port interface; and wherein the
second side of the pressure port interface includes a pressure
fitting.
12. The modular pressure sensor of claim 11, wherein the pressure
fitting on the second side of the pressure port interface is one of
either a swage fitting or a threaded fitting.
13. The modular pressure sensor of claim 11, wherein pressure
sensor device is configured to disconnect from the pressure port
interface by releasing a mounting device that secures the substrate
to the pressure port interface.
14. The modular pressure sensor of claim 11, further comprising:
wherein the cover is brazed to the ceramic substrate; and wherein a
getter is formed on a side of the cover internal to the cavity.
15. The modular pressure sensor of claim 11, wherein the pressure
sensor device further comprises: at least one integrated circuit
device co-located with the pressure sensor die within the cavity,
wherein the at least one integrated circuit device comprises one of
a memory device, an analog-to-digital converter, a digital signal
processor, a voltage regulator, or an amplifier.
16. The modular pressure sensor of claim 11, wherein the ceramic
substrate further comprises: a low temperature co-fired ceramic, a
high temperature co-fired ceramic, or combinations thereof; at
least one stress isolation trench, wherein the at least one stress
isolation trench forms part of the vacuum cavity; and a recessed
portion; wherein a thermal coefficient of expansion of the ceramic
substrate is approximately matched to a thermal coefficient of
expansion of the pressure sensor die; and wherein the cover
comprises silicon and is thermoelectrically bonded to the ceramic
substrate such that the cavity is formed over the recessed
portion.
17. A pressure sensor apparatus comprising: a ceramic substrate
comprising a recessed portion and a pressure port; a silicon cover
thermoelectric bonded to the ceramic substrate such that a volume
between the silicon cover and the recessed portion form a reference
cavity; a silicon pressure sensor die thermoelectric bonded to the
ceramic substrate over the pressure port and within the reference
cavity, wherein a thermal coefficient of expansion of the silicon
pressure sensor die is approximately equal to a thermal coefficient
of expansion of the ceramic substrate; a plurality of electrical
pads on a first side of the ceramic substrate, wherein the silicon
pressure sensor die is electrically connected to at least one of
the electrical pads; and a plurality of electrical connectors
mounted to the ceramic substrate external to the reference cavity,
the plurality of electrical connectors electrically coupled to the
plurality of electrical pads; and wherein the ceramic substrate
includes at least one mounting element configured to secure a
pressure port interface to a second side of the ceramic substrate
in a position around the pressure port.
18. The pressure sensor apparatus of claim 17, further comprising:
an analog-to-digital converter mounted on the ceramic substrate
within the reference cavity, wherein the analog-to-digital converts
an analog pressure signal from the silicon pressure sensor device
into a digital signal; and a digital signal processor mounted on
the ceramic substrate within the reference cavity, wherein the
digital signal processor processes the digital signal.
19. The pressure sensor apparatus of claim 17, further comprising:
a memory device mounted on the ceramic substrate within the vacuum
cavity, wherein the memory device stores error correction
coefficients for the silicon pressure sensor die.
20. The pressure sensor apparatus of claim 17, wherein the ceramic
substrate further comprises a first stress isolation trench located
on a first side of the silicon pressure sensor die and a second
stress isolation trench located on a second side of the silicon
pressure sensor die.
Description
BACKGROUND
[0001] High accuracy pressure sensors are applicable to many
different types of applications and usually require precise
sealing. A typical legacy pressure sensor maintains a vacuum cavity
between a header and a pressure sensor die. Often the pressure
sensor and its attachment must be custom designed for a particular
application and is not easily replaced. Electrical pins extend into
a reference cavity and are subject to mechanical loading, possibly
leading to leaking of the cavity. Molecular off-gassing into the
cavity ages and degrades the performance of the pressure sensor.
Additionally, legacy pressure sensor packages are also constrained
with respect to the size of the pressure sensor die (with different
header designs for different pressure sensor die sizes) and
mounting the pressure sensor package can be difficult due to
inconvenient placement of the electrical pins.
[0002] For the reasons stated above and for other reasons stated
below which will become apparent to those skilled in the art upon
reading and understanding the specification, there is a need in the
art for a modular sensor package with improved stress isolation,
reduced aging effects, and is adaptable for many end-use
applications.
SUMMARY
[0003] The embodiments of the present invention provide methods,
systems, and apparatus' for modular pressure sensor devices and
will be understood by reading and studying the following
specification.
[0004] Modular pressure sensor devices are provided. In one
embodiment, a pressure sensor device comprises a substrate having a
pressure port that extends through the substrate from a first side
of the substrate to a second side of the substrate. A pressure
sensor die is attached to the first side of the substrate, forming
a seal over the pressure port on the first side of the substrate. A
cover is attached to the first side of the substrate over the
pressure sensor die, forming a sealed cavity wherein the pressure
sensor die is located within the cavity. A plurality of electrical
connectors is mounted to the substrate external to the cavity, the
plurality of electrical connectors electrically coupled to the
pressure sensor die. The substrate also includes at least one
mounting element configured to secure a pressure port interface to
the second side of the substrate in a position around the pressure
port.
DRAWINGS
[0005] Embodiments of the present invention can be more easily
understood and further advantages and uses thereof more readily
apparent, when considered in view of the description of the
preferred embodiments and the following figures in which:
[0006] FIG. 1 is a simplified block diagram of one embodiment of
the present invention of a modular sensor package;
[0007] FIGS. 2A and 2B are views of one embodiment of the present
invention of a modular sensor package;
[0008] FIG. 2C is a view of one embodiment of the present invention
of a ceramic substrate;
[0009] FIGS. 3 is a side view of another embodiment of the present
invention of a modular sensor package;
[0010] FIGS. 4A and 4B are views of another embodiment of the
present invention of a modular sensor package;
[0011] FIG. 5 is a side view of another embodiment of the present
invention of a modular sensor package;
[0012] FIGS. 6A and 6B are views of another embodiment of the
present invention of a modular sensor package; and
[0013] FIG. 7 is a flowchart illustrating one embodiment of a
method of the present invention for providing a pressure
sensor.
[0014] In accordance with common practice, the various described
features are not drawn to scale but are drawn to emphasize features
relevant to the present invention. Reference characters denote like
elements throughout figures and text.
DETAILED DESCRIPTION
[0015] In the following detailed description, reference is made to
the accompanying drawings that form a part hereof, and in which is
shown by way of specific illustrative embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized and that logical, mechanical and electrical changes
may be made without departing from the scope of the present
invention. The following detailed description is, therefore, not to
be taken in a limiting sense.
[0016] Embodiments of the present invention provide a modular
sensor packaging approach that is easily adapted for different
pneumatic connection requirements while addressing the sealing and
stress isolation concerns that typically affect pressure sensors.
As will be discussed in more detail below, a modular sensor
packaging approach for silicon-based pressure sensor dies provides
very low correctable errors, integral stress isolation to reduce
errors, interface to different end-use requirements, and supports
low cost manufacturing strategies.
[0017] Some embodiments of the modular sensor package implement
swappable pressure port interfaces suitable for various
applications. Embodiments of the present invention provide a
pressure sensor whose electrical connections do not pierce through
reference cavity of the pressure sensor. Other embodiments of the
present invention improve the performance of the pressure sensor
through co-locating electronic circuitry with a pressure sensor
die. Embodiments of the present invention employ different bonding
techniques to improve the functionality of the modular sensor
package.
[0018] FIG. 1 is a simplified block diagram of one embodiment of
the present invention of a modular sensor package 100. The modular
sensor package 100 comprises a sensor device 110 and a pressure
port interface 150. Further illustrated in FIG. 1, electrical pins
120 provide electrical connectivity for pressure sensor 110. As
will be discussed in greater detail below, pressure port interface
150 is designed to mechanically couple sensor device 110 to a
pressure port 115. Pressure port interface 150 may include one of a
myriad of pressure port fittings such as, but not limited to, a
threaded fitting or a swage fitting. Accordingly, the particular
pressure port interface 150 is selected to match the pressure port
fitting used at pressure port 115. Pressure port interface 150 then
provides a path for delivering the particular process delivered at
pressure port 115 (for example, gas or liquid) to sensor device 110
so that sensor device 110 can measure the pressure of the
process.
[0019] FIG. 1 illustrates the modular sensor packaging approach of
embodiments of the present invention. Pressure port interface 150
can be selected based on the type of port fitting used at pressure
port 115. A particular sensor device 110 can be selected based on
the type of process being delivered to pressure port 115 as well as
the particular pressure range and sensitivity requirements that
sensor device 110 is expected to cover. Thus, a range of different
configurations of sensor devices 110 and pressure port interfaces
150 can be achieved. Further, should a sensor device 110 fail, or
requirements change, pressure sensor 110 can be removed and
replaced without the need to remove pressure port interface 150
from pressure port 115.
[0020] In alternate embodiments, pressure port interface 150
comprises stainless steel, aluminum, Inconel 756, or any other
material compatible with the pressure requirements at pressure port
115 and parameters of the particular installation environment, such
as temperature.
[0021] FIGS. 2A and 2B are views of one embodiment of the present
invention of a modular sensor package shown generally at 200. FIG.
2A is a side view and FIG. 2B is a top view of the modular pressure
sensor package 200. Modular sensor package 200 comprises a sensor
device 205 and a pressure port interface 250. Sensor device 200
further comprises a ceramic substrate 220, a pressure sensor die
230, a cover 236, and a plurality of electrical connectors 234. A
recess 222 formed in ceramic substrate 220 holds pressure sensor
die 230 and defines a sealed cavity 240 when cover 236 is bonded to
the substrate 220.
[0022] In alternate embodiments, cover 236 is bonded to ceramic
substrate 220 using either thermal electric (TE) bonding or
brazing. TE bonding is a form of ionic bonding used to bond a first
material (such as silicon) to a second material (such as certain
glasses, including ceramic or pyrex). Transport of mobile ions from
the silicon to the second material forms an air tight bond. Where
TE bonding is used, part of the surface of ceramic substrate 220 is
prepared for TE bonding and TE bonding is used to make sealed
attachments of ceramic substrate 220 to pressure sensor die 230 and
cover 236. Brazing is an attachment process where a filler material
is heated to liquid form and placed between two parts, where it
forms a seal upon cooling. In one embodiment where brazing is used,
the interfaces of ceramic substrate 220 to pressure sensor die 230,
cover 236, and pressure port interface 250 are brazed. TE bonding
has an advantage over brazing in that it will not break down when
used for high temperature applications (for example, in excess of
275.degree. C.), provides excellent vacuum integrity, and
simplifies the process of assembling the modular sensor package
200. Further, in alternate embodiments, cover 236 acts as a second
level pressure containment boundary should the integrity of
pressure sensor die 230 fail. In one such embodiment, cover 236
would be subject to high pressures in excess of 2.5
kilopound/in.sup.2 (KSI). In alternate embodiments, cover 236
comprises silicon, Kovar (a nickel-cobalt ferrous alloy), Invar (a
nickel-steel alloy), Nispan (a nickel-chrome-iron alloy), or any
other suitable material. In an embodiment where TE bonding is used,
cover 236 is generally straight and can support some of the
electrical connectors 234.
[0023] In one embodiment, ceramic substrate 220 comprises a low
temperature co-fired ceramic (LTCC) material that closely or
approximately matches the thermal coefficient of expansion (TCE) of
silicon. In other embodiments, ceramic substrate 220 comprises a
composite of different types of co-fired ceramics. For example, one
embodiment of ceramic substrate 220 comprises an intermingled mix
of high temperature co-fired ceramics (HTCC) and low temperature
co-fired ceramics, wherein different sections of the ceramic
substrate 220 are selected for the primary use of that portion of
ceramic substrate 220. For example, sections of the ceramic
substrate 220 that bond to the cover 236 or pressure port interface
250 are selected for strength, brazability, etc. and the portion of
ceramic substrate 220 that pressure sensor die 230 is bonded to is
approximately matched to the TCE of the pressure sensor die 230. In
one embodiment, part or all of ceramic substrate 220 comprises a
glass with having a higher anneal and melting point than the
temperature required for TE bonding (for example, SD-2 glass
available from HOYA Corp.).
[0024] In one embodiment, ceramic substrate 220 is comprised of
composite materials that approximately match the TCE of the
different ceramics it comprises to each other. In another
embodiment, the TCEs of ceramic substrate 220 and pressure sensor
die 230 are also approximately matched. This improves stress
isolation, reducing non-critical errors of the pressure sensor 205,
and eliminates the need for a separate precision and stress
isolation component used in legacy sensor packages.
[0025] In one embodiment, ceramic substrate 220 comprises at least
two stress isolation trenches 226-1 and 226-2 formed within cavity
240. In the particular embodiment shown in FIG. 2A, stress
isolation trenches 226-1 and 226-2 are situated underneath wire
bonds 244. Stress isolation trenches 226-1 and 226-2 are located
within cavity 240 to reduce the amount of stress transmitted to the
pressure sensor die 230 from the ceramic substrate 220. The
thickness and depth of stress isolation trenches 226-1 and 226-2
are selected for the particular embodiment of the modular sensor
package 200. Generally, the closer the TCEs of ceramic substrate
220 and pressure sensor die 130 match, the smaller stress isolation
trenches 226-1 and 226-2 can be for a given reduction in stress. In
the embodiment shown in FIG. 2A, the first stress isolation trench
226-1 is formed on a first side of the pressure sensor die 230 and
the second stress isolation trench 226-2 is formed on a second side
of the pressure sensor die 230. Ceramic substrate 220 also
comprises a pressure port 228 that exposes the pressure sensor die
230 to the pressure of the pressure port such as pressure port 115
in FIG. 1.
[0026] Ceramic substrate 220 further comprises a pressure port 228
that exposes pressure sensor die 230 to the pressure of the process
received at pressure port interface 250. Pressure port 228 extends
completely through ceramic substrate 220 directly below the
pressure sensor die 230. Pressure sensor die 230 measures the
pressure received at pressure port 228 and converts those
measurements into electrical signals provided via a plurality of
electrical connectors, shown at 234.
[0027] Electrical connectors 234 are coupled, either directly or
indirectly, to pressure sensor die 230. In one embodiment, a
plurality of electrical pads 242 surround the pressure sensor die
230 inside the cavity 240 and are coupled to pressure sensor die
230 via a plurality of wire bonds 244. In one embodiment, the
electrical pads 342 comprise gold, but may alternately comprise any
other suitable electrically conducting material.
[0028] Turning to FIG. 2C, a view of one embodiment of the present
invention of a ceramic substrate 220 is shown. Ceramic substrate
220 further comprises wire traces 208 which provide electrical
conductivity between the electrical connector 234 and the
electrical pad 242 through ceramic substrate 220. By providing
electrical connectivity between the external electrical connectors
234 and the electrical pads 242 via traces 208 within substrate
220, embodiments of the present invention avoid the need to
penetrate the seal of cavity 240, which avoids one potential source
of seal leakage into cavity 240. In one embodiment, wire traces 208
are comprised of embedded layers of metallization that aid in
maintaining the structural integrity of ceramic substrate 220 when
through vias 209 are formed in ceramic substrate 220.
[0029] Returning to FIG. 2A, because cavity 240 is sealed by a
cover 236, cavity 240 acts as a reference vacuum against which
pressure sensor die 230 measures the pressure received at pressure
port 228. In the embodiment of FIG. 2A, cavity 240 is held at an
approximate vacuum and is referred to as a vacuum reference
pressure. In other embodiments, cavity 240 contains one or more
gasses of what is referred to as a gas reference pressure. In
either case, the pressure within cavity 240 is referred to herein
simply as a reference pressure. The accuracy of pressure
measurements provided by sensor 200 is at least partially dependent
on the pressure integrity of cavity 240. That is, the accuracy of
pressure data provided over the lifetime of the modular sensor
package 200 will be stable when the reference pressure in cavity
240 is stable over time and environmental factors. In one
embodiment, to improve pressure integrity, a getter 238, a layer of
reactive material, is applied to a surface of the cover 236 that is
internal to the cavity 240. In one embodiment, the getter 238 is
applied using sputtering techniques, for example. The getter 238
protects vacuum integrity through absorbing spurious gas molecules
that are released over time into cavity 240.
[0030] Pressure sensor die 230 is a transducer that converts
mechanical flexing of the pressure sensor die 230 due to pressure
changes into electrical signals. Pressure sensor die 230 flexes in
response to the difference between the processes pressure to which
it is exposed through pressure port 228 and the reference pressure
in cavity 240. The electrical signals are transmitted to connection
pads 242 via wire bonds 244. In one embodiment, the pressure sensor
die 230 is also TE bonded to ceramic substrate 220.
[0031] In the embodiment shown in FIG. 2A, ceramic substrate 220 is
an LTCC material with a TCE equal to approximately that of silicon.
The strength of ceramic substrate 220 is approximately 17 to 40 KSI
and the theoretical TE bond strength between the silicon (for
example, of pressure sensor die 230) and ceramic substrate 220
approaches this strength. In one implementation of modular sensor
package 200, the pressure ported through the pressure port 228 is
approximately 1 KSI.
[0032] In one embodiment, ceramic substrate 220 is connected to
pressure port interface 250 with mounting screws 210-1 and 210-2
that pass through ceramic substrate 220 via through holes 212-1 and
212-2. In one embodiment, ceramic substrate 220 comprises a
metallization layer 208 that strengthens ceramic substrate 220
where through holes 212-1 and 212-2 are formed. In other
embodiments, ceramic substrate 220 attaches to pressure port
interface 250 with fold over tabs, which may take up less physical
space than mounting screws 210-1 and 210-2. In other embodiments,
modular sensor package 200 use other attachment means.
[0033] In the embodiment shown in FIG. 2A, pressure port interface
250 comprises a threaded connection 256 for coupling pressure port
interface 250 to an external threaded fitting. Pressure port
interface 250 further comprises a pressure port opening 252
providing access to pressure port 228. Pressure port interface 250
further comprises a ring shaped seal 254 (such as an o-ring) that
seals pressure port interface 250 against ceramic substrate 220,
while leaving space for pressure port 228 to remain exposed to the
process pressure. For embodiments in high temperature applications,
ring shaped seal 254 is a non-organic seal (such as a braze ring).
In one embodiment, pressure port interface 250 further comprises
holes 260-1 through 260-4 for further securing pressure port
interface 250 to an external device or system.
[0034] In the embodiment shown in FIG. 2A, electrical connectors
234 are mounted on a first side 202 of ceramic substrate 220 and
the pressure port interface 250 is mounted on a second side 204 of
ceramic substrate 220. Thus, electrical connectors 234 face in one
direction while pressure port interface 250 faces in an opposing
direction. This configuration provides improved stress isolation
and reduces the mechanical load on the electrical connectors 234
over the legacy sensor package because more of the mechanical load
on modular pressure sensor 200 is taken by pressure port interface
250 when the process pressure is high and during installation of
the modular pressure sensor 200.
[0035] Exemplary dimensions of ceramic substrate 220 are
approximately 0.500 inches by 0.375 inches. Exemplary dimensions of
pressure port interface 250 are approximately 1.000 inches by 0.500
inches. However, other dimensions are contemplated. Ceramic
substrate 220 accommodates various dimensions of pressure sensor
die 230 within the scope of the dimensions of ceramic substrate 220
without changing the outer configuration around pressure sensor die
230.
[0036] FIGS. 3 is a side view of another embodiment of the present
invention of a modular sensor package shown generally at 300
comprising the sensor device 205 described above with respect to
FIGS. 2A-2C, coupled with a pressure port interface 350. In
contrast with threaded pressure port interface 250 of FIG. 2A,
pressure port interface 350 has a tube extension 356 that can be
attached to a swage fitting. Otherwise, the combination of sensor
device 205 with pressure port interface 350 performs as described
above, demonstrating the reconfiguration benefits provided by
embodiments of the present invention.
[0037] FIGS. 4A and 4B are views of another embodiment of the
present invention of a modular sensor package shown generally at
400. Modular sensor package 400 comprises a pressure sensor 405
coupled to a pressure port interface 450. Pressure sensor 405
further comprises a ceramic substrate 420, a pressure sensor die
430, a cover 436, and a plurality of electrical connectors 434. In
one embodiment, ceramic substrate 420 further comprises stress
isolation trenches 426-1 and 426-2. Pressure sensor 405 is secured
to pressure port interface 450 using screws 410-1 through 410-4.
Also as described above, process pressure received at pressure port
interface 450 is communicated to pressure sensor die 430 via port
opening 428.
[0038] In the embodiment of FIG. 4A, cover 436 is a shaped cover
(for example, rounded). Modular sensor package 400 utilizes a
brazed seal to adhere cover 436 to substrate 420. In one
embodiment, cover 436 is a Kovar material with a low TCE. The
temperature during brazing is controlled such that it does not
exceed the temperature limits of wire bonds or the pads attached to
substrate 420. As would be appreciated by one of ordinary skill in
the art upon reading this specification, a brazed cover 436 has an
advantage over TE bonding when the surface of substrate 420 cannot
be polished for TE bonding, or due to considerations such as cost
restrictions.
[0039] Cover 436 is braized to substrate 420 and forms a cavity 440
in the gap between cover 436 and substrate 420. In this embodiment,
the ceramic substrate 420 does not have a recessed portion. The
pressure sensor die 430, wide bonds 444, and electrical pads 442
are located within the cavity 420 and operate as described above
with respect to their counterparts in FIGS. 2A and 2B. In the
embodiment of FIG. 4A, pressure port interface 450 comprises a
threaded connection 456 and is otherwise identical to pressure port
interface 250 described above with respect to FIG. 2A.
[0040] FIG. 5 is a side view of another embodiment of the present
invention of a modular sensor package 500 comprising the sensor
device 405 described above with respect to FIGS. 4A and 4B, coupled
with pressure port interface 350 from FIG. 3. Otherwise, the
combination of sensor device 405 with pressure port interface 350
performs as described above. As demonstrated above, modular
pressure sensor packages 200, 300, 400, and 500 easily adapt to
combinations of sensor devices with pressure port interfaces
facilitating a variety of applications by selecting the appropriate
combination for the application.
[0041] FIGS. 6A and 6B are views of another embodiment of the
present invention of a modular sensor package shown generally at
600. Modular sensor package 600 comprises a ceramic substrate 620,
a pressure sensor die 630, a cover 636, a plurality of electrical
pins 634, electrical pads 642, mounting holes 610-1 through 610-4
for mounting screws or the like, and a pressure port interface 650.
The ceramic substrate 620 comprises stress isolation trenches 626-1
and 626-2, screws 610-1 through 610-4, a raised portion 638, and
port opening 628 within the raised portion 638. Pressure sensor die
630 is TE bonded to the raised portion 628. A cavity 640 is formed
between cover 636 and ceramic substrate 620.
[0042] Modular sensor package 600 further comprises integrated
circuit devices 632 mounted on substrate 620 within cavity 640.
Co-locating integrated circuit devices with the pressure sensor die
within a vacuum cavity reduces aging effects on the integrated
circuit devices. In this embodiment, modular sensor package 600
co-locates the integrated circuit devices 632 and the pads 642 with
the pressure sensor die 630 inside the cavity 640. In embodiments
of the modular sensor package 100 where the integrated circuit
devices 132 are co-located with the pressure sensor die 130 in the
cavity 140, the pads 142 are also connected to the integrated
circuit devices 132, either through wire bonds 144 or wire traces
124. The integrated circuit devices 132 resolve the electrical
signals into pressure data that indicates the difference between
the ambient pressure and the environment of the cavity 140. In
another embodiment, the modular sensor package 600 also includes
one or more transistors or capacitors mounted on substrate 620
within cavity 640.
[0043] FIG. 6B is a top view of pressure sensor package 600. Cover
636 is only partially shown so that the internal cavity 640 is
depicted. Inside the cavity between cover 636 and ceramic substrate
620 is mounted a pressure sensor die 630, wire bond pads 642, and
an assortment of integrated circuit devices 632. The integrated
circuit devices 632 comprise a digital signal processor 662, an
analog-to-digital converter 664, a voltage regulator 666,
amplifying device 668, and a memory device 670. A suitable memory
device 670 comprises a form of non-volatile memory, including by
way of example, semiconductor memory devices (such as Erasable
Programmable Read-Only Memory (EPROM) and Electrically Erasable
Programmable Read-Only Memory (EEPROM). The integrated circuit
devices are electrically connected with wire bonds to wire bond
pads 642.
[0044] In one embodiment of modular sensor package 600, the output
of pressure sensor die 630 is buffered using a series of resistors
(referred to as temperature bridge resistors) on pressure sensor
die 630 for temperature compensation. Amplifying device 668 (such
as, for example, an operational amplifier) uses the temperature
bridge resistors to provide the buffered output of the pressure
sensor die 630. One embodiment of the output is a wheatstone bridge
output as well as a low impedance buffered output that includes
temperature compensation.
[0045] Memory 670 stores error correction coefficients that are
used to make error corrections to output of the pressure sensor die
630. Each pressure sensor die 630 has specific error correction
coefficients that are kept with modular sensor package 600 and
typically calibrated during or after manufacture. When modular
sensor package 600 is swapped with a new one (for example, during a
field change if the original modular sensor package 600 fails), the
new pressure sensor does not have to be calibrated because it
already contains the error correction coefficients for that
pressure sensor die.
[0046] Voltage regulator 666 provides a nearly constant voltage
supply that improves the stability of pressure sensor 630. The
analog-to-digital converter 664 converts the analog output of
pressure sensor die 682 into a digital word. The digital signal
processor 662 processes the digital word that the analog-to-digital
converter 664 generates.
[0047] Performance of the high precision modular sensor package 600
is improved through reduced aging due to improved stability, and
modular sensor package 600 is more able to achieve a predetermined
percent drift specifications (for example, approximately 0.02 to
0.05% over 10 years). The circuitry of the embodiment shown in FIG.
6B is in proximity to the pressure sensor die 630, in a low noise
environment, has reduced contamination problems, and is conditioned
for the specific pressure sensor die 630.
[0048] FIG. 7 is a flowchart illustrating one embodiment of a
method 700 of the present invention for providing a pressure
sensor. Method 700 begins at 710 with preparing a ceramic
substrate. In one embodiment, preparing the ceramic substrate
includes fabricating the ceramic substrate. Typically, the ceramic
substrate is fabricated as a large panel for multiple pressure
sensors. The material of the ceramic substrate is selected and
matched to the TCE of the pressure sensor die. In different
embodiments, the ceramic substrate comprise LTCC material, HTCC
material, or an intermingled combination of co-fired ceramics. The
ceramic substrate is shaped and metalized for its particular design
(including making through vias, wire traces, pressure port, stress
isolation chambers and a recess for the pressure sensor die).
[0049] Once the ceramic substrate is fabricated, the surfaces of
the ceramic substrate that are used for TE bonding are polished.
For example, the surfaces of the ceramic substrate that attach to a
silicon cover and a silicon pressure sensor die are polished.
Polishing improves the TE bonding for a strong, leak tight joint.
After polishing, wire bond pads are applied. For example, gold or
aluminum metallization is performed on the ceramic substrate to
create the wire bond pads. The ceramic substrate is fired to bond
its layers together into homogeneous ceramic substrate, which also
creates vacuum integrity. In another embodiment of the method
further including metallization of the ceramic substrate for as a
stress distribution layer to support mounting screws. In one
embodiment, the stress distribution layer is relatively thick when
the cover is TE bonded. If the cover is a brazed cover, a stress
distribution layer is not used when the mounting screws are
incorporated into the cover. At this stage, in one embodiment, the
method 700 also applies a getter to absorb low molecular weight
gasses emitted from different areas inside the vacuum cavity. In
one embodiment, preparing the ceramic substrate further comprise
mounting integrated circuit devices onto the fired ceramic
substrate.
[0050] Once the ceramic substrate is prepared, the method proceeds
to 720 with attaching a pressure sensor die to the ceramic
substrate. The attachments are made with inorganic materials in
order to reduce offgassing and increase the operating temperature
range of the pressure sensor. Wire bonding is performed to connect
the pressure sensor die to the wire bond pads. This is performed on
the panelized substrate using, for example, an automated pick and
place wire bonding machine.
[0051] The method proceeds to 730 with bonding a cover to the
ceramic substrate to form a sealed cavity. The cover is either TE
bonded or brazed to the ceramic substrate. The panelized approach
can be maintained all the way through characterization testing,
which reduces costs.
[0052] The method proceeds to 740 with electrically coupling
electrical pins mounted external to the cavity with the pressure
sensor die through the substrate. In one embodiment, one or more of
the electrical pins are further electrically coupled to the
integrated circuit devices mounted within the cavity. In one
embodiment, some of the pins are attached to the ceramic substrate
directly and some are attached to the cover. In one embodiment, the
electrical pins are electrically coupled to the pressure sensor die
and/or the integrated circuit devices mounted within the cavity via
wire traces embedded in the substrate.
[0053] The method proceeds to 750 with attaching a pressure port
interface to the pressure sensor. The pressure port interface
adapts the pressure sensor to couple to a pressure port and will
comprise a compatible mechanical fitting (for example, a threaded
fitting or a swage fitting) to form a pressure seal with the
pressure port. The pressure port interface includes a cavity that
exposes the pressure sensor to the pressure delivered at the
pressure port so that pressure measurements can be obtained. In one
embodiment, the electrical pins are attached to the pressure sensor
on a side of the ceramic substrate opposing the pressure port
interface to avoid placing unnecessary stresses on the electrical
pins.
[0054] The embodiments described herein provide a unique pressure
sensor packaging approach for silicon-based pressure sensors that
has very low correctable errors, integral stressed isolation, and a
modular approach to interfacing the pressure port for different
end-use requirements, and support low cost manufacturing
strategies. The modularity of the embodiments is extendable to
accommodate various levels of integrated circuit devices
complexity. The embodiments described herein are suitable for use
in any pressure sensor application, such as avionics systems,
factories with high vibrations, ships, or any other system or
apparatus that uses pressure data.
[0055] Producing hermetic sealing for entry and exit of electrical
connections with TE bonding improves the reliability of the
pressure seal while simultaneously providing a substantial
reduction in the manufacturing cost. Embodiments described herein
also are adaptable to pneumatic connection requirements, give high
performance, are flexible, and are operable over a higher
temperature range. The embodiments described herein also have a
smaller footprint than legacy pressure sensors, resulting in
reduced weight and size that is particularly advantages for
applications requiring low weight and size, such as aerospace.
Embodiments described herein also reduce the possibility that a
fractured electrical connector causes the loss of the reference
pressure because the electrical connectors do not extend through
the cavity that holds the reference pressure.
[0056] A number of embodiments of the invention defined by the
following claims have been described. Nevertheless, it will be
understood that various modifications to the described embodiments
may be made without departing from the spirit and scope of the
claimed invention. Features and aspects of particular embodiments
described herein can be combined with or replace features and
aspects of other embodiments. Accordingly, other embodiments are
within the scope of the following claims.
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