U.S. patent application number 09/726723 was filed with the patent office on 2002-05-30 for protective cover and attachment method for moisture sensitive devices.
This patent application is currently assigned to GE Medical Systems Global Technology Company, LLC. Invention is credited to Maydanich, Fyodor I., Shvetskiy, Yakov.
Application Number | 20020063218 09/726723 |
Document ID | / |
Family ID | 24919741 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020063218 |
Kind Code |
A1 |
Maydanich, Fyodor I. ; et
al. |
May 30, 2002 |
Protective cover and attachment method for moisture sensitive
devices
Abstract
A radiation imaging device includes a scintillator, a cover and
an imager substrate. A photodetector array comprising a plurality
of photodetectors is s disposed on the imager substrate. The cover
is hermetically bonded to the substrate with a sealant. The cover
has outer sidewalls and a top side connecting the outer sidewalls.
In attaching to the substrate, the cover is disposed on the imager
substrate to surround the scintillator. A curable sealant is
applied along the outer surface of the cover. The sealant is then
cured to hermetically bond the cover to the substrate.
Inventors: |
Maydanich, Fyodor I.;
(Wauwatosa, WI) ; Shvetskiy, Yakov; (Sunnyvale,
CA) |
Correspondence
Address: |
WILLIAM COLLARD
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Assignee: |
GE Medical Systems Global
Technology Company, LLC
|
Family ID: |
24919741 |
Appl. No.: |
09/726723 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
250/370.11 ;
250/370.12 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/0002 20130101; Y02E 10/52 20130101; H01L 27/14618
20130101; H01L 27/14663 20130101; G01T 1/2018 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
250/370.11 ;
250/370.12 |
International
Class: |
G01T 001/24 |
Claims
What is claimed is:
1. A radiation imaging device comprising: (a) an imager substrate;
(b) a photodetector array comprising a plurality of photodetectors
disposed on said imager substrate; (c) a scintillator comprising a
moisture sensitive material disposed adjacent to said photodetector
array; and (d) a cover having outer sidewalls hermetically bonded
to the substrate with a sealant and a top side connecting said
outer sidewalls, said cover comprising a material being
substantially impervious to moisture and having a low degree of
radiation attenuation so as to protect the scintillator from
moisture intrusion.
2. The device according to claim 1 wherein said photodetector array
comprises a direct detection array comprising a plurality of direct
detection materials selected from the group consisting of mercury
iodide (HgI.sub.2) and lead iodide (PbI.sub.2) disposed on said
imager substrate.
3. The device according to claim 1 wherein said cover has a
coefficient of thermal expansion substantially the same as the
coefficient of thermal expansion of the imager substrate.
4. The device according to claim 1 wherein said cover is produced
from a highly compacted particulate and continuous fiber reinforced
metal alloy.
5. The device according to claim 1 wherein the sealant comprises
continuous beads of a material curable at room temperature.
6. The device according to claim 1 wherein said scintillator
comprises cesium iodide.
7. The device according to claim 1 wherein said cover has an x-ray
attenuation below 5%.
8. The device according to claim 1 wherein said cover has an x-ray
attenuation from 1% to 3%.
9. The device according to claim 1 wherein said cover has an x-ray
attenuation from 1.5% to 2.5%.
10. A method of attaching a protective cover to a radiation imaging
device comprising: (a) providing a cover comprising a material
substantially impervious to moisture and having a low degree of
radiation attenuation, said cover having outer sidewalls and a top
sidewall connecting said outer sidewalls; (b) disposing the cover
on an imager substrate of the imaging device to surround a
scintillator of the imaging device; (c) applying a curable sealant
along the outer surface of the cover; and (d) curing the sealant to
hermetically bond the cover to the substrate so as to protect the
scintillator from moisture intrusion.
11. The method according to claim 10 wherein the sealant is cured
by ultraviolet light
12. The method according to claim 10 wherein the cover is produced
from a highly compacted particulate and continuous fiber reinforced
metal alloy.
13. The method according to claim 10 wherein the sealant comprises
continuous beads of a material curable at room temperature.
14. The method according to claim 10 wherein the scintillator
comprises cesium iodide.
15. A digital x-ray imager comprising: (a) an imager substrate; (b)
a direct detection array comprising a plurality of direct
photodetectors disposed on said imager substrate; (c) a
scintillator comprising cesium iodide disposed adjacent to said
direct detection array; and (d) a cover in the shape of a picture
frame hermetically bonded to the substrate with continuous beads of
an ultraviolet light cured sealant, said cover being x-ray
transmissive and substantially impervious to moisture so as to
protect the scintillator from moisture intrusion.
16. The digital x-ray imager of claim 15 wherein said direct
photodetectors comprise direct detection materials selected from
the group consisting of mercury iodide (HgI.sub.2) and lead iodide
(PbI.sub.2).
17. The digital x-ray imager of claim 15 wherein said cover has a
coefficient of thermal expansion substantially the same as the
coefficient of thermal expansion of the imager substrate.
18. The digital x-ray imager of claim 15 wherein said cover is
produced from a highly compacted particulate and continuous fiber
reinforced metal alloy.
19. The digital x-ray imager of claim 15 wherein said cover has an
x-ray attenuation below 5%.
20. The digital x-ray imager of claim 15 wherein said cover has an
x-ray attenuation from 1% to 3%.
21. The digital x-ray imager according to claim 15 wherein said
cover has an x-ray attenuation from 1.5% to 2.5%.
22. A method of attaching a protective cover to a digital x-ray
imager comprising: (a) providing a cover in the shape of a picture
frame comprising an x-ray transmissive material substantially
impervious to moisture; (b) disposing the cover on an imager
substrate of the digital x-ray imager to surround a cesium iodide
scintillator of the x-ray imager; (c) applying continuous beads of
an ultraviolet light curable sealant along the outer surface of the
cover; and (d) curing the sealant to hermetically bond the cover to
the substrate so as to protect the scintillator from moisture
intrusion.
23. The method according to claim 22 wherein said cover is produced
from a highly compacted particulate and continuous fiber reinforced
metal alloy.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to radiation imaging systems.
More particularly, the invention relates to a protective cover for
an x-ray imager suitable for use in medical diagnostic
applications. A method of attaching the cover to the upper surface
of the x-ray imager's substrate is also provided.
[0003] 2. The Prior Art
[0004] A number of protective covers for radiation imaging systems
used for medical and industrial purposes are known. For example,
U.S. Pat. No. 5,132,539 to Kwasnick et al. relates to a planar
x-ray imager having a moisture-resistant sealing structure.
[0005] Such sealing covers are desirable to protect the
scintillator material of the imaging system from moisture
absorption. The covers are especially desirable when the end use
environment has a high humidity content. For example, cesium
iodide, a common scintillator material, is hygroscopic and exhibits
a tendency to absorb moisture from the atmosphere around it. In so
doing, the material becomes hydrolyzed with a consequent
degradation in its luminescent properties. In radiation imaging
systems, the radiation typically comprises x-ray or gamma rays.
This radiation is absorbed in the scintillator material, resulting
in the generation of photons of light. These photons in turn are
detected by photodetectors to generate an electrical output signal.
This signal is processed to drive a visual display device or other
equipment to analyze the detected electromagnetic radiation
patterns. Chemical reactions occur continually between the cesium
oxide scintillator and the atmospheric moisture of the radiation
detector's end use environment. These reactions lead to the
degradation of the detector resolution. They also lead to the
deterioration of the conversion factor and the decline of
detector/device reliability.
[0006] Known digital x-ray detectors employ a cover/epoxy
seal/x-ray imager interface to isolate the detector's scintillator
from atmospheric moisture. The x-ray imaging device includes a
photodetector array disposed on a substrate with a scintillator
disposed on the substrate. A cover is bonded to the substrate with
an epoxy bead so as to extend over the scintillator.
[0007] This existing cover/seal/substrate interface construction
allows some ambient moisture penetration through the epoxy bead
driven by moisture diffusion through the epoxy. Moreover, the
process of cover attachment to the substrate suffers from a lack of
consistent and repeatable output. The attachment process requires
extensive and complicated process fixtures. It also requires a high
degree of manual dexterity, and a process duration of 48-72
hours.
[0008] Hence, a cover and attachment method is needed that will
reduce moisture penetration into the cesium iodide array from
diffusion.
BRIEF SUMMARY OF THE INVENTION
[0009] A radiation imaging device is provided with a cover/imager
substrate interface to isolate the scintillator from the end use
environment. The device includes a scintillator comprising a
moisture sensitive material, such as cesium iodide. A photodetector
array comprising a plurality of photodetectors is disposed on an
imager substrate. A cover is hermetically bonded to the substrate
with a sealant. The cover is generally in the form of a "picture
frame" or open-ended box. The cover has first and second surfaces
and a third surface connecting the first and second surfaces. The
cover comprises a material being substantially impervious to
moisture and having a low degree of radiation attenuation.
[0010] A method of attaching the protective cover to a radiation
imaging device is also provided. In accordance with this method,
the cover is disposed on the imager substrate to surround the
scintillator. A curable sealant is then applied continuously along
the outer surface of the cover. The sealant is then cured to
hermetically bond the cover to the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other objects and features of the present invention will
become apparent from the following detailed description considered
in connection with the accompanying drawings. It should be
understood, however, that the drawings are designed for the purpose
of illustration only and not as a definition of the limits of the
invention.
[0012] In the drawings, wherein similar reference characters denote
similar elements throughout the several views:
[0013] FIG. 1 is a schematic cross-sectional diagram of the sealing
scheme of a prior art radiation imaging device.
[0014] FIG. 2 is a schematic cross-sectional diagram of a radiation
imaging device in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] Referring to FIG. 1, a simplified diagram of an existing
sealing scheme is shown. In FIG. 1, an x-ray imaging device 10
includes a photodetector array (not shown) disposed on a substrate
7. A scintillator 5 is disposed on substrate 7. A cover 1 is bonded
to substrate 7 with epoxy bead 3 so as to extend over scintillator
5.
[0016] Now referring to FIG. 2, the radiation imaging device 20 of
a preferred embodiment is shown. Device 20 includes a photodetector
array 30 disposed on a substrate 28 and a scintillator 26 disposed
adjacent to the photodetector array. A cover 22 is hermetically
bonded to substrate 28 and extends over scintillator 26. The
photodetector array is coupled to a processing circuit (not shown).
The processing circuit processes the electrical signals for use in
display and analysis equipment (not shown).
[0017] Photodetector array 30 comprises a plurality of
photodetectors 32 arranged and electrically connected in a pattern,
typically rows and columns. The photodetectors are disposed on
imager substrate 28 to form an array. The array can be of any size
and shape appropriate for the use of imaging device 20. For
example, the array may be adapted for medical analysis of
particular portions of the body. The photodetectors are
advantageously photodiodes and alternatively may comprise other
known solid state x-ray detectors, such as direct detection arrays,
i.e. Hgl.sub.2 (mercury iodide) and PbI.sub.2 (lead iodide)
photodetector devices. A connector (not shown) carries the
electrical signals generated in the photodetectors to the
processing circuit.
[0018] Scintillator 26 is positioned adjacent to photodetector
array 30 and arranged so that light photons from the scintillator
readily pass into photodetectors. An optical index matching
substance may be provided in a separate layer between the two
arrays. Other materials which efficiently transfer photons from the
scintillator to the photodetectors may also be used. As illustrated
in FIG. 2, scintillator 26 comprises a substantially homogeneous
block of scintillator material. Alternatively, separate
scintillator elements (not shown) may be diced, or cut, from a
larger block of scintillator material. Scintillator elements may
also be separately grown or deposited in columnar structures using
known methods. For example, vapor deposition or sputtering can be
used for this purpose. Scintillator 26 comprises a first end
surface 34 through which incident x-ray or gamma radiation 36
enters the scintillator. A second end surface 38 is opposite to the
first end surface. The light photons pass through surface 38 to the
adjoining photodetector array 30. Scintillator 26 further has outer
peripheral edges 40 extending between first end surface 34 and
second end surface 38. Cesium iodide is typically used to form
scintillator 26. Alternatively, other known scintillating materials
can be used.
[0019] Cover 22 is disposed around that portion of photodetector
array 30 receiving the light generated by the scintillators. As
shown in FIG. 2, cover 22 has outer sidewalls extending between a
top side 46 of cover 22 and the top surface of substrate 28. Left
and right sides 42, 44 (from the viewer's perspective) of the outer
sidewalls are shown in FIG. 2 but it is to be understood that the
outer sidewalls extend around the outer surface of cover 22. Top
side 46 connects the outer sidewalls to close the cover at the top.
The bottom portion of the cover, that is the open face or inner
surface of cover 22 is closed by the surface of substrate 28. This
"open face" cover/substrate interface drastically reduces the
direct moisture path from the end use environment to the
scintillator local ambient environment. Due to the interposition of
solid wall material between the end use and local environments,
diffusion through the epoxy seal is practically eliminated. Unlike
the prior art, moisture has to travel both through the epoxy seal
and the outer sidewalls of the cover. Thus, the "open face"
cover/substrate interface prevents continuous chemical reactions
between the scintillator material, for example, cesium iodide, and
atmospheric moisture. This arrangement results in improved x-ray
detector reliability. In comparison to prior art sealing schemes,
moreover, the seal is for less susceptible, if at all, to
shrinkage, thermoexpansion and viscosity changes which caused
cracks and leakages in prior sealing schemes.
[0020] In order to be used for x-ray detection applications, the
cover's material should have a low degree of x-ray attenuation.
Preferably, the x-ray attenuation is below 3-5%, desirably from 1
to 3%, and preferably from 1.5 to 2.5%. The coefficient of thermal
expansion of the cover advantageously closely matches the
coefficient of thermal expansion of substrate 28. The cover
material should also have sufficient stiffness to assure the
imager's structural integrity.
[0021] To produce the material and cover configuration, a highly
compacted particulate and continuous fiber reinforced metal alloy
can be used. For example, a metal alloy produced by the Advanced
Pressure Infiltration Casting process available from Metal Matrix
Cast Composites, Inc., 101 Clematis Ave., Waltham, Mass. 02453-7012
can be used. Cover materials disclosed in U.S. Pat. No. 5,132,539
to Kwasnick et al. may also be used.
[0022] To form the cover/substrate interface, cover 22 is first
disposed over substrate 28. Continuous beads of a sealant 24 are
then formed along the outer surface of cover 22. Preferably,
sealant 24 comprises a moisture resistant adhesive such as an
epoxy. For example, EP38 available from Master Bond, Inc., 154
Hobart Street, Hackensack, N.J. 07601, for curing at room
temperature can be used. Alternatively, other known adhesives such
as acrylics and acrylated urethanes can be used such as adhesives
3103 and 3525 available from LOCTITE Corporation, 1001 Trout Brook
Crossing, Rocky Hill, Conn. 06067-3910, for curing by ultraviolet
(UV) light. Other less preferred sealants include UV15-7, UV15-7SP4
available from Master Bond, Inc.
[0023] Cover 22 is hermetically bonded to substrate 28 and extends
above scintillator 26. Cover 22 forms a seal which prevents
moisture in liquid or vapor from passing through the cover. Cover
22 has no strong interaction with the radiation to be detected by
the imaging device. It allows a maximum amount of the incident
radiation from source 36 to enter scintillator 26 without
absorption or scattering.
[0024] The "picture frame" cover/substrate interface allows for a
higher degree of precision. It affords repeatable alignment between
the cover's inner surfaces and the edges of the scintillator's
cesium iodide active array. The shape and positioning of the cover
and a simple fixture utilization for sealant bead formation defines
the interface. The "open face" cover/substrate's common boundary
significantly simplifies the entire sealant application procedure.
It enables an ease of use for manual and semiautomatic means of
sealant application during the manufacturing process.
[0025] In attaching to a radiation imaging device, cover 22 is
disposed on imager substrate 28 of imaging device 20 to surround
scintillator 26. A curable sealant 24 is then applied along the
outer surface of cover 22. Sealant 24 is then cured, preferably
under a nitrogen atmosphere, to hermetically bond cover 22 to
substrate 28. For improved productivity, a UV cured sealant is used
which leads to a substantial reduction in process duration (from
48-72 hours to 1-2 hours).
[0026] Thus, a "picture frame" shaped cover and a method of
attachment is provided. The cover is radiation transmissive and
minimizes scattering of light away from the scintillator. The cover
outer surface is attached to the upper surface of an x-ray imager's
substrate. The cover resembles a box with an open top which is
placed upside down on the imager's substrate. The cover/imager's
substrate interface removes an unreliable moisture barrier between
the cesium iodide and the end use environment. It also eliminates
the degradation of x-ray detector resolution and conversion factor
due to moisture impact on the cesium iodide. In addition, the
detector reliability is improved.
[0027] While preferred embodiments of the present invention have
been shown and described, it is to be understood that many changes
and modifications may be made thereunto without departing from the
spirit and scope of the invention as defined in the appended
claims.
* * * * *