专利汇可以提供Sealed symmetric multilayered microelectronic device package with integral windows专利检索,专利查询,专利分析的服务。并且A sealed symmetric multilayered package with integral windows for housing one or more microelectronic devices. The devices can be a semiconductor chip, a CCD chip, a CMOS chip, a VCSEL chip, a laser diode, a MEMS device, or a IMEMS device. The multilayered package can be formed of a low-temperature cofired ceramic (LTCC) or high-temperature cofired ceramic (HTCC) multilayer processes with the windows being simultaneously joined (e.g. cofired) to the package body during LTCC or HTCC processing. The microelectronic devices can be flip-chip bonded and oriented so that the light-sensitive sides are optically accessible through the windows. The result is a compact, low-profile, sealed symmetric package, having integral windows that can be hermetically-sealed.,下面是Sealed symmetric multilayered microelectronic device package with integral windows专利的具体信息内容。
We claim:1. A sealed symmetric package having at least two integral windows for packaging at least two microelectronic devices, comprising a first package and a second package joined together;wherein the first package comprises:a first electrically insulating plate comprising a multilayered material having a first surface, an opposing second surface, and a first aperture disposed through said first plate;an electrically conductive metallized trace disposed on the second surface of said first plate;an integral window disposed across the first aperture and bonded to said first plate, for providing optical access to a microelectronic device disposed within said assembly; anda second electrically insulating plate having a third surface, an opposing fourth surface, and a second aperture disposed through said second plate;an electrically conductive metallized trace disposed on the fourth surface of the second plate;wherein the first plate is attached to the second plate by joining the second surface to the third surface; andwherein the second aperture is larger than the first aperture; andwherein the second package comprises a package substantially identical to the first package; andwherein the first package is inverted and bonded to the second package to form a sealed symmetric package.2. The sealed symmetric package of claim 1, wherein, in the first package, the window substantially fills the first aperture.3. The sealed symmetric package of claim 2, wherein, in the first package, the aperture-filling window is formed by casting a castable window material directly into the first aperture.4. The sealed symmetric package of claim 3, wherein, in the first package, the castable window material comprises molten glass that solidifies after casting.5. The sealed symmetric package of claim 3, wherein, in the first package, the castable window material comprises a liquid polymer that solidifies after casting.6. The sealed symmetric package of claim 1, wherein, in the first package, said window is bonded to the first surface.7. The sealed symmetric package of claim 1, wherein, in the first package, the geometry of the joint between the window and the first plate comprises an encased joint geometry.8. The sealed symmetric package of claim 1, wherein, in the first package, said window is bonded to a lip recessed inside of the first plate.9. The sealed symmetric package of claim 8, wherein, in the first package, said window is mounted flush with the first surface of the first plate.10. The sealed symmetric package of claim 1, wherein, in the first package, said window comprises an optically transparent material selected from the group consisting of glass, sapphire, fused silica, plastic, and polymer.11. The sealed symmetric package of claim 1, wherein, in the first package, further comprising a surface treatment to improve wettability and adhesion of mating surfaces.12. The sealed symmetric package of claim 1, wherein, in the first package, said window comprises an anti-reflection coating.13. The sealed symmetric package of claim 1, wherein, in the first package, said window comprises means for filtering selected wavelengths of light.14. The sealed symmetric package of claim 1, wherein, in the first package, the second plate comprises the same multilayered material as the first plate.15. The sealed symmetric package of claim 14, wherein said multilayered material comprises a high-temperature cofired ceramic multilayered material fired at a temperature in the range of 1300° C. to 1800° C.16. The sealed symmetric package of claim 14, wherein said multilayered material comprises a low-temperature cofired ceramic multilayered material fired at a temperature in the range of 600° C. to 1000° C.17. The sealed symmetric package of claim 14; wherein said multilayered material comprises a laminated multilayered printed wiring board composition.18. The sealed symmetric package of claim 1, further comprising a bonding material consisting of a material selected from the group consisting of a hermetic sealant and an adhesive.19. The sealed symmetric package of claim 1, further comprising a hermetic sealant selected from the group consisting of a braze alloy, a frit glass compound, a glass-ceramic composite a glass-polymer compound, a ceramic-polymer compound, and a solder alloy.20. The sealed symmetric package of claim 1, further comprising an adhesive selected from the group consisting of an epoxy resin, a polyimide adhesive, a silicone adhesive, and a urethane adhesive.21. The sealed symmetric package of claim 1, wherein, in the first package, said window further comprises a lens for optically transforming the light that passes through the window.22. The sealed symmetric package of claim 21, wherein, in the first package, said lens is attached to said window.23. The sealed symmetric package of claim 21, wherein, in the first package, said lens is integrally formed with said window.24. The sealed symmetric package of claim 21, wherein, in the first package, further comprising an array of binary optic lenslets made integral with said window.25. The sealed symmetric package of claim 1, wherein, in the first package, further comprising an electrically-switched optical modulator attached to said first package, for modulating light passing through an aperture.26. The sealed symmetric package of claim 25, wherein, in the first package, wherein said electrically-switched optical modulator comprises a lithium niobate window.27. The sealed symmetric package of claim 1, further comprising electrically conductive vias disposed within said electrically insulating plates, for conducting electrical signals in a direction generally perpendicular to the plane of said plates.28. The sealed symmetric package of claim 1, further comprising at least one microelectronic device mounted within said symmetric package.29. The sealed symmetric package of claim 28, wherein said microelectronic device is a device selected from the group consisting of a semiconductor chip, a CCD chip, a CMOS chip, a VCSEL chip, a laser diode, a MEMS device, and a IMEMS device.30. The sealed symmetric package of claim 28, wherein said microelectronic device is mounted to the second surface of the first package.31. The sealed symmetric package of claim 28 wherein said microelectronic device is flip-chip mounted to the second surface of the first package.32. The sealed symmetric package of claim 28, wherein said microelectronic device comprises a light-sensitive side.33. The sealed symmetric package of claim 27, wherein said light-sensitive side is mounted facing said window of the first package.34. The sealed symmetric package of claim 28, further comprising a seal disposed in-between said microelectronic device and the second surface of the first package.35. The sealed symmetric package of claim 1, wherein the ambient air inside said sealed symmetric package has been substantially removed and replaced with at least one gas other than air.36. The sealed symmetric package of claim 1, further comprising a first microelectronic device, flip-chip mounted to the second surface of the first package; and a second microelectronic device, flip-chip mounted to the second surface of the second package.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional application of allowed U.S. patent application “Microelectronic Device Package with an Integral Window, Peterson et al., Ser. No. 09/571,335, filed May 16, 2000 now U.S. Pat. No. 6,384,473 which is incorporated Herein by reference.
FEDERALLY SPONSORED RESEARCH
The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation.
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of microelectronics, and more specifically to packaging of microelectronic devices in a package having an integral window.
Many different types of microelectronic devices require a window to provide optical access and protection from the environment. Examples of optically-interactive semiconductor devices include charge-coupled devices (CCD), photo-sensitive cells (photocells), solid-state imaging devices, and UV-light sensitive Erasable Programmable Read-Only Memory (EPROM) chips. All of these devices use microelectronic devices that are sensitive to light over a range of wavelengths, including ultraviolet, infrared, and visible. Other types of semiconductor photonic devices emit light, such as laser diodes and Vertical Cavity Surface-Emitting Laser (VCSELS), which also need to pass light through a protective window.
Microelectromechanical systems (MEMS) and Integrated MEMS (IMEMS) devices (e.g. MEMS devices combined with Integrated Circuit (IC) devices) can also require a window for optical access. Examples of MEMS devices include airbag accelerometers, microengines, microlocks, optical switches, tiltable mirrors, miniature gyroscopes, sensors, and actuators. All of these MEMS devices use active mechanical and/or optical elements. Some examples of active MEMS structures include gears, hinges, levers, slides, tilting mirrors, and optical sensors. These active structures must be free to move or rotate. Optical access through a window is required for MEMS devices that have mirrors and optical elements. Optical access to non-optically active MEMS devices can also be required for inspection, observation, and performance characterization of the moving elements.
Additionally, radiation detectors which detect alpha, beta, and gamma radiation, use “windows” of varying thickness and materials to either transmit, block, or filter these energetic particles. These devices also have a need for windows that transmit or filter radiation to and from the device, while at the same time providing physical and environmental protection.
The word “transparent” is broadly defined herein to include transmission of radiation (e.g. photons and energetic particles) covering a wide range of wavelengths and energies, not just UV, IR, and visible light. Likewise, the word “window” is broadly defined herein to include materials other than optically transparent glass, ceramic, or plastic, such as thin sheets,.of metal, which can transmit energetic particles (e.g. alpha, beta, gamma, and light or heavy ions).
There is a continuing need in the semiconductor fabrication industry to reduce costs and improve reliability by reducing the number of fabrication steps, while increasing the density of components. One approach is to shrink the size of packaging. Another is to combine as many steps into one by integrating operations. A good example is the use of cofired multilayer ceramic packages. Unfortunately, adding windows to these packages typically increases the complexity and costs.
Hermetically sealed packages are used to satisfy more demanding environmental requirements, such as for military and space applications. The schematic shown in
FIG. 1
illustrates a conventional ceramic package for a MEMS device, a CCD chip, or other optically active microelectronic device. The device or chip is die-attached face-up to a ceramic package and then wirebonded to interconnect inside of the package. Metallized circuit traces carry the electrical signal through the ceramic package to electrical leads mounted outside. A glass window is attached as the last step with a frit glass or solder seal. Examples of conventional ceramic packages include Ceramic Dual In-Line Package (CERDIP), EPROM and Ceramic Flatpack designs.
Although stronger, ceramic packages are typically heavier, bulkier, and more expensive to fabricate than plastic molded packages. Problems with using wirebonding include the fragility of very thin wires; wire sweep detachment and breakage during transfer molding; additional space required to accommodate the arched wire shape and toolpath motion of the wirebond toolhead; and the constraint that the window (or cover lid) be attached after the wirebonding step. Also, attachment of the window as the last step can limit the temperature of bonding the window to the package.
FIG. 2
illustrates schematically a conventional molded plastic (e.g. encapsulated) microelectronic package. The chip is attached to a lead frame, and a polymer dam prevents the plastic encapsulant from flowing onto the light-sensitive area of the chip during plastic transfer molding. The window is generally attached with a polymer adhesive. Problems with this approach include the use of fragile wirebonded interconnections; and plastic encapsulation, which does not provide hermetic sealing against moisture intrusion.
Flip-chip mounting of semiconductor chips is a commonly used alternative to wirebonding. In flip-chip mounting the chip is mounted face-down and then reflow soldered using small solder balls or “bumps” to a substrate having a matching pattern of circuit traces (such as a printed wiring board). All of the solder joints are made simultaneously. Excess spreading of the molten solder ball is prevented by the use of specially-designed bonding pads. Flip-chip mounting has been successfully used in fabricating Multi-Chip Modules (MCM's), Chip-on-Board, Silicon-on-Silicon, and Ball Grid Array packaging designs.
Flip-chip mounting has many benefits over traditional wirebonding, including increased packaging density, lower lead inductance, shorter circuit traces, thinner package height, no thin wires to break, and simultaneous mechanical die-attach and electrical circuit interconnection. Another advantage is that the chips are naturally self-aligning due to surface tension when using molten solder balls. It is also possible to replace the metallic solder bumps With bumps, or dollops, of an electrically-conductive polymer or epoxy (e.g. silver-filled epoxy). Flip-chip mounting avoids potential problems associated with ultrasonic bonding techniques that can impart stressful vibrations to a fragile (e.g. released) MEMS structure.
Despite the well-known advantages of flip-chip mounting, this technique has not been widely practiced for packaging of MEMS devices, Integrated MEMS (IMEMS), or CCD chips because attaching the chip face-down to a solid, opaque substrate prevents optical access to the optically-active, light-sensitive surface.
The cost of fabricating ceramic packages can be reduced by using cofired ceramic multilayer packages. Multilayer packages are presently used in many product categories, including leadless chip carriers, pin-grid arrays (PGA's), side-brazed dual-in-line packages (DIP's), flatpacks, and leaded chip carriers. Depending on the application, 5-40 layers of dielectric layers can be used, each having printed signal traces, ground planes, and power planes. Each signal layer can be connected to adjacent layers above and below by conductive vias passing through the dielectric layers.
Electrically conducting metallized traces, thick-film resistors, and solder-filled vias or Z-interconnects are conventionally made by thick-film metallization techniques, including screen-printing. Multiple layers are printed, vias-created, stacked, collated, and registered. The layers are then joined together (e.g. laminated) by a process of burnout, followed by firing at elevated temperatures. Burnout at 350-600° C. first removes the organic binders and plasticizers from the substrate layers and conductor/resistor pastes. After burnout, these parts are fired at much higher temperatures, which sinters and densifies the glass-ceramic substrate to form a dense and rigid insulating structure. Glass-forming constituents in the layers can flow and fill-in voids, corners, etc.
Two different cofired.ceramic systems are conventionally used, depending on the choice of materials: high-temperature cofired ceramic (HTCC), and low-temperature cofired ceramic (LTCC). HTCC systems typically use alumina substrates; are printed with molybdenum-manganese or tungsten conducting traces; and are fired at high temperatures, from 1300° C. to 1800° C. LTCC systems use a wide variety of glass-ceramic substrates; are printed with Au, Ag, or Cu metallizations; and are fired at lower temperatures, from 600° C. to 1300° C. After firing, the semiconductor die is attached to the fired HTCC (or LTCC) body; followed by wirebonding. Finally, the package is lidded and sealed by attaching a metallic, ceramic, or glass cover lid with a braze, a frit glass, or a solder seal, depending on the hierarchy of thermal processing and on performance specifications.
Use of cofired multilayer ceramic structures for semiconductor packages advantageously permits a wide choice of geometrical designs and processing conditions, as compared to previous use of bulk ceramic pieces (which typically had to be cut and ground from solid blocks or bars). Ceramic packages with high-temperature seals are generally stronger and have improved hermeticity, compared to plastic encapsulated packages. It is well known to those skilled in the art that damaging moisture can penetrate polymer-based seals over time. Also, metallized conductive traces are more durable than freestanding wire bond segments, especially when the traces are embedded and protected within a layer of insulating material.
In summary, conventional methods and designs for packaging of light-sensitive microelectronic devices attach the window (or cover lid containing a window) after completing the steps of die attachment and wirebonding of the chip or MEMS device to the package. Many processing steps are used, which can expose the fragile MEMS structures to particulate contamination and mechanical damage during packaging.
What is needed is a packaging process that minimizes the number of times that a MEMS device is handled and exposed to temperature cycles and different environments, which can possibly lead to contamination of the device. This can be accomplished by performing as many of the package fabrication steps as possible before mounting the MEMS device. What is needed, then, is a packaging process that attaches the window to the package before mounting the chip to the package. It is also desired that the window be attached to the package body at a high temperature to provide a strong, hermetic bond between the window and the body. What also is needed is a method where the MEMS device faces away from the cover lid, so that contamination is reduced when the cover lid is attached last.
Electrical interconnections from the chip to the package are needed that are stronger and less fragile than conventional wirebonds. What also is needed is a package having a high degree of strength and hermeticity. In some cases, it is also desired to stack back-to-back multiple chips, of different types (e.g. CMOS, MEMS, etc.) inside of a single, windowed-package.
Use of the phrase “MEMS devices” is broadly defined herein to include “IMEMS” devices, unless specifically stated otherwise. The word “plastic” is broadly defined herein to include any type of flowable, dielectric composition, including polymer compounds and spin-on glass-polymer compositions. The phrases “released MEMS it structures”, “released MEMS elements”, and “active MEMS elements” and “active MEMS structures” are used interchangeably to refer to a device having freely-movable structural elements, such as gears, pivots, hinges, sliders, tilting mirrors; and also to exposed active elements such as chemical sensors, flexible membranes, and beams with thin-film strain gauges, which are used in accelerometers and pressure sensors.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form part of the specification, illustrate various examples of the present invention and, together with the description, serve to explain the principles of the invention.
FIG. 1
shows a schematic cross-section view of a conventional ceramic microelectronic package where the window or cover lid is attached last, after the microelectronic device has been joined (face-up) to the base and wirebonded.
FIG. 2
shows a schematic cross-section view of a conventional plastic molded microelectronic package, where the microelectronic device, lead frame, and window are encapsulated in a plastic body by a transfer molding process.
FIG. 3A
shows a schematic cross-section view of a first example of a microelectronic package according to the present invention, with the package having an integral window attached to a ceramic body including an first (lower) plate, a second (upper) plate, and an attached cover lid.
FIG. 3B
shows a schematic cross-section view of the second example of a microelectronic package according to the present invention, with the package having an integral window cofired with a cofired multilayered assembly of twelve individual layers, and an attached cover lid.
FIG. 4A
shows a schematic cross-section view of a third example of a microelectronic package according to the present invention that is similar to the second example of
FIG. 3B
, but with a cofired window substantially filling up the aperture through the first plate.
FIG. 4B
shows a schematic cross-section view of a fourth example of a microelectronic package according to the present invention that is similar to the second example of
FIG. 3B
, but with a cofired window mounted to a recessed lip located inside of the first plate, recessed from the second surface of the first plate.
FIG. 4C
show a schematic cross-section view of a fifth example of a microelectronic package according to the present invention that is similar to the second example of
FIG. 3B
, but with a window mounted flush to the bottom surface of the first plate.
FIG. 5
shows a schematic cross-section view of a sixth example of a microelectronic package according to the present invention, with the package having an integral window cofired to a cofired multilayered assembly including an first (bottom) plate, a second (middle) plate, a third (top) plate, and an attached cover lid, for packaging a pair of stacked chips, including a MEMS chip flip-chip mounted to the first plate, and a second chip attached to the backside of the MEMS chip, wirebonded to the second plate.
FIG. 6A
shows a schematic cross-section view of a seventh example of a microelectronic package according to the present invention that is similar to the first example of
FIG. 3A
, but with the cover plate removed, and also having a second package, substantially identical to the first example of
FIG. 3A
(also without a cover plate), where the second package has been inverted and joined to the first package, thereby forming a substantially symmetric package.
FIG. 6B
shows a schematic cross-section view of an eighth example of a microelectronic package according to the present invention that is similar to the first example of
FIG. 3A
, but with the cover plate removed, and also having a second package, substantially identical to the first example of
FIG. 3A
(also without a cover plate), where the second package has been stacked above the first package and joined to the first package, thereby forming a stacked, double-package.
FIG. 6C
shows a schematic cross-section view of a ninth example of a microelectronic package according to the present invention that is similar to the sixth example of
FIG. 5
, but with the cover plate removed, and also having a second package, substantially identical to the first example of
FIG. 5
(also without a cover plate), where the second package has been inverted and joined to the first package, thereby forming a substantially symmetric package.
FIG. 6D
shows a schematic cross-section view of a tenth example of a microelectronic package according to the present invention that is similar to the first example of
FIG. 5
, but with the cover plate removed, and also having a second package, substantially identical to the first example of
FIG. 5
(also without a cover plate), where the second package has been stacked above the first package and joined to the first package, thereby forming a stacked, double-package.
FIG. 7
shows a schematic top view along line
1
—
1
of
FIG. 3A
of a sixteenth example of a microelectronic package for housing at least one microelectronic device according to the present invention, illustrating examples of the electrically conducting metallized traces located on the upper surface of the first plate, including interconnect bumps, interior bond pads, exterior bond pads, and a conductive via.
FIG. 8
shows a schematic top view of a seventeenth example of a microelectronic package for housing at least one microelectronic device according to the present invention, wherein the package can be a multi-chip module (MCM), including multiple integral windows and multiple microelectronic devices in a two-dimensional array.
FIG. 9
shows a schematic side view of a eighteenth example of a microelectronic package for housing at least one microelectronic device according to the present invention, wherein the window further comprises a lens for optically transforming light passing through the window.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a package for housing at least one microelectronic device, comprising a hollow assembly of stacked, electrically insulating plates and an integral window.
It should be noted that the examples of the present invention shown in the figures are sometimes illustrated with the window facing down, which is the preferred orientation during flip-chip bonding. However, those skilled in the art will understand that the completed package e can be oriented for use with the window facing upwards. It should also be noted that all of the figures show only a single microelectronic device, illustrated as a microelectronic device or pair of chips. It is intended that the method and apparatus of the present invention should be understood by those skilled in the art as applying equally to a plurality of chips or devices packaged in a one-dimensional or a two-dimensional array, as in a multi-chip module (MCM), including multiple windowed-compartments, and including having a window on either side of the package.
FIG. 3A
shows a schematic cross-section view of a first example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, comprising a hollow assembly
10
of stacked, electrically insulating plates. The assembly
10
of
FIG. 3A
has an interior interconnect location
12
disposed on an interior surface of hollow assembly
10
, and an exterior interconnect location
14
disposed on an exterior surface of assembly
10
. Assembly
10
further comprises a first plate
16
. Plate
16
has a first surface
20
, an opposing second surface
18
, and a first aperture
22
through, plate
16
. Plate
16
also has an electrically conductive metallized trace
24
disposed on surface
18
, for conducting an electrical signal between interior interconnect location
12
and exterior interconnect location
14
. Plate
16
further comprises a first window
26
bonded to plate
16
, for providing optical access to a microelectronic device
100
that could be disposed within assembly
10
.
In
FIG. 3A
, assembly
10
further comprises a second plate
30
, which has a third surface
34
, an opposing fourth surface
32
, and a second aperture
36
through plate
30
for providing physical access to insert device
100
into package
8
. Surface
18
of plate
16
is bonded to the surface
34
of plate
30
to form assembly
10
. At least one lateral dimension of aperture
36
is slightly larger than the corresponding lateral dimension of aperture
22
. Aperture
22
is substantially aligned with aperture
36
. The lateral dimensions of aperture
36
are slightly larger than the lateral dimensions of chip or device
100
, so that chip or device
100
can fit inside of aperture
36
.
In
FIG. 3A
, window
26
is attached flush to plate
16
. The attachment can comprise a first seal
38
. Other mounting arrangements will be disclosed later. The shape of aperture
22
and aperture
36
can be polygonal (e.g. square or rectangular) or circular. Aperture
22
can have a different shape than aperture
36
. The horizontal surfaces of device
100
, plate
16
, plate
18
, and window
26
all can be substantially coplaner. Microelectronic device
100
can comprise a microelectronic device
100
.
In
FIG. 3A
, microelectronic device
100
can be flip-chip mounted (e.g. flipped facedown, with optically active area
109
of chip or device
100
facing towards window
26
) to surface
18
of plate
16
. The method of flip-chip mounting is well-known to those skilled in the art. Surface
18
can comprise a bond pad
44
electrically connected to metallized trace
24
at interior interconnect location
12
. Microelectronic device
100
can include interconnect bumps pre-attached to chip or device
100
. Alternatively, surface
18
can comprise an interconnect bump
46
, connected either to metallized trace
24
or to bond pad
44
at interior interconnect location
12
. Interconnect bump
46
can comprise an electrically conductive material (e.g. gold, gold alloy, aluminum, solder, and silver-filled epoxy) for electrically connecting chip or device
100
to metallized trace
24
or bond pad
44
. Alternatively, bump
46
can comprise a non-conducting, adhesive material (e.g. epoxy resin, polyimide, silicone, or urethane) for providing mechanical attachment of chip or device
100
to surface
18
.
In
FIG. 3A
, package
8
can include a bond pad
28
attached to assembly
10
at exterior interconnect location
14
. Bond pad
28
can be electrically connected to metallized trace
24
. Package
8
can also include an electrical lead
40
attached to assembly
10
at exterior interconnect location
14
. Lead
40
can be electrically connected to metallized trace
24
. Optionally, lead
40
can be attached to bond pad
28
. Assembly
10
can also comprise an electrically conductive via
54
, which can be in electrical communication with metallized trace
24
. Via
54
can be oriented perpendicular to surface
18
, and can be disposed from surface
18
to surface
16
. Via
54
can be made electrically conducting by filling hole
54
with solder or other flowable, electrically conducting material.
In
FIG. 3A
, assembly
10
can include a cover lid
42
attached to surface
32
of plate
30
. Attachment of cover lid
42
can complete the packaging of semiconductor chip or device
100
inside of a sealed package
8
. Cover lid
42
can include a second window (not shown in FIG.
3
A), for providing optical access through aperture
36
. Optionally, the ambient air inside of sealed package
8
can be substantially removed before attaching cover lid
42
, and replaced with at least one gas other than air. This other gas can include an inert gas (e.g. argon, nitrogen, or helium). Helium can be easily detected by a conventional helium leak detector, thereby providing information on the hermetic quality of the joints and seals in package
8
. The level of humidity can also be adjusted prior to sealing package
8
with cover lid
42
.
In
FIG. 3A
, plate
16
is attached to plate
18
. This attachment can comprise a second seal
48
disposed in-between surface
18
and surface
34
. Seal
48
can have an annular shape. Likewise, the attachment between cover lid
42
and plate
30
can comprise a third seal
50
. Seal
50
can also have an annular shape. The bonding material used for either seals
38
,
48
or
50
can comprise a hermetic sealant (e.g. a braze alloy, a frit glass compound, a glass-ceramic composite, a glass-polymer compound, a ceramic-polymer compound, or a solder alloy) or an adhesive material (e.g. an epoxy resin, a polyimide adhesive, a silicone adhesive, or a urethane adhesive). Selection of a particular material for seal
38
,
48
or
50
should take into consideration the hierarchy of thermal processing for the entire packaging process. Here, “thermal hierarchy” means that the highest temperature processes (e.g. sintering, joining, etc.) are performed first, followed by progressively lower temperature processes, with the lowest temperature process being performed last in the sequence of fabrication steps.
Window
26
can comprise an optically transparent material (e.g. a borosilicate glass, a quartz glass (i.e. fused silica), a low-iron, a leaded glass, a tempered glass, a low thermal-expansion glass, or a transparent ceramic, such as sapphire). Alternatively, a transparent plastic or polymer-based material can be used (e.g. PMMA). Some plastics are transparent in the UV spectrum. Silicon can be used for windows that are transparent in the IR spectrum. Preferably, the window's coefficient of thermal expansion (CTE) is about equal to the CTE of plate
16
. Alternatively, the mismatch in CTE between window
26
and plate
16
can be chosen avantageously so that window
26
is placed in compression. Window
26
can optionally comprise optical quality properties (e.g. purity, flatness, and smoothness).
Window
26
can comprise means for filtering selected wavelengths of light. Coloring dyes, or other elements, can be added to the glass or plastic formulations to form windows that can filter light, as is well-known to the art. Anti-reflection coatings can be applied to the surface or surfaces of window
26
to reduce reflection and/or increase transmission. Also, surface treatments (e.g. thin-film coatings or controlled surface roughness) can be applied to the periphery of window
26
in order to improve the wettability of molten solders and brazes, and to improve the adhesion of window
26
to plate
16
. The same surface treatments can also be applied to the mating surfaces of other pairs of surfaces to be joined, including plates
16
and
30
, and cover lid
42
. Window
26
can also be made of a metal or metal alloy, for use in packaging of a microelectronic device used for detecting energetic particles.
In
FIG. 3A
, assembly
10
includes plates comprising an electrically insulating material (e.g. a ceramic, a polymer, a plastic, a glass, a glass-ceramic composite, a glass-polymer composite, a resin material, a fiber-reinforced composite, a glass-coated metal, or a printed wiring board composition) well-known to the art. The ceramic material can comprise alumina, beryllium oxide, silicon nitride, aluminum nitride, titanium nitride, titanium carbide, or silicon carbide. Fabrication of ceramic parts can be performed by processes well-known to the art (e.g. slip casting, machining in the green state, cold-isostatic pressing (CIP) followed by hot-isostatic pressing (HIP) or sintering, and uniaxially hot/cold pressing, or rapid forging). Fabrication of plastic and polymer parts can be performed by processes well-known to the art (e.g. transfer molding, injection molding, and machining of printed wiring board (PWB) sheets).
For severe environments, ceramic packages are generally stronger and more hermetic than plastic encapsulated packages. The preferred construction of a microelectronic package with an integral window can use cofired ceramic multilayers. The multiple, stacked ceramic layers are formed by casting a blend of ceramic and glass powders, organic binders, plasticizers, and solvents into sheets or tapes. The organic components provide strength and flexibility to the green (unfired) sheets during substrate personalization and fabrication. Burnout at a relatively low temperature (e.g. 350-600° C.) removes the organic binders and plasticizers from the substrate layers and conductor/resistor pastes. After burnout, these parts are fired at much higher temperatures, which sinters and densifies the glass-ceramic substrate to form a dense, rigid, insulating structure. Glass-forming constituents in the layers can flow and avantageously fill-in voids, corners, etc.
Two different cofired ceramic systems are conventionally used, depending on the choice of materials: high-temperature cofired ceramic (HTCC), and low-temperature cofired ceramic (LTCC). If the ratio of ceramic to glass is high (9/1, or greater), the green substrate layer can only be sintered (e.g. densified) at high firing temperatures (e.g. 1300 to 1800° C.). Consequently, the thick-film pastes (e.g. to form metallized trace
24
) that are typically cofired with the substrate also have to withstand these high temperatures, such as tungsten, or alloys of molybdenum and manganese. The dielectric consists of glass fillers in a ceramic matrix. This system is referred to as HTCC. Alternatively, the dielectric can be a ceramic-filled glass matrix, which can be sintered at much lower firing temperatures (e.g. 600° C. to 1300° C.). Thick-film metallization can comprise high-conductivity metals, such as gold, silver, copper, silver-palladium, and platinum-gold. This system is referred to as LTCC.
If hermetic packaging is not required, then polymer-based materials can be used. Multilayer printed wiring board (PWB) materials can be used for constructing assembly
10
. In this system, metallized trace
24
is fabricated by using an etched-foil process, well-known to those skilled in the art. Similar to cofired ceramic multilayers, the multiple layers of PWB composition are stacked and laminated under pressure and temperature in a single bonding step (e.g. co-bonded) to form a multilayered assembly
10
.
FIG. 3B
shows a schematic cross-section view of a second example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, comprising a hollow assembly
10
of stacked, electrically insulating plates comprising multiple layers of ceramic tape stacked and laminated under simultaneous pressure and temperature (e.g. cofiring) to form a multi-layered cofired ceramic assembly
10
. Such a construction technique readily accommodates the preferred stepped interior-surface profile, as required to hold window
26
and chip or device
100
, since the individual layers are easily punched-out or cut (e.g. via a laser, waterjet, or mechanical press) into shapes of varying sizes that can be stacked and cofired to form multi-layered cofired ceramic assembly
10
. For example,
FIG. 3B
shows an arrangement for integrating window
26
into first plate
16
comprising an encased joint geometry
39
(where the edges of window
26
are embedded inside plate
16
). If a bulk ceramic plate were used, it would be very difficult to manufacture such a reentrant, recessed feature for housing window
26
therein. However, by using a laminated, multilayered construction, this is relatively easy to do.
In
FIG. 3B
, assembly
10
comprises twelve individual layers of ceramic tape stacked and laminated to form a monolithic, unitized body having an integral window
26
. The part of assembly
10
grouped as plate
16
′ comprises six individual layers (e.g. sheets) of glass-ceramic tape (e.g. layers
61
,
62
,
63
,
64
,
65
, and
66
). Likewise, the part of assembly
10
grouped as plate
30
′ comprises six additional individual layers (e.g. layers
67
,
68
,
69
,
70
,
71
, and
72
). Each layer can be individually personalized with the appropriate inside and outside dimensions. Metallized trace
24
can be deposited on the upper surface of layer
66
(corresponding to surface
18
of
FIG. 3A
) prior to stacking of the individual layers. Window
26
can be inserted into the stack of layers after the surrounding layers
61
,
62
,
63
, and
64
have been stacked and registered. The remaining eight layers (e.g.
65
-
72
) can be stacked and registered after window
26
has been inserted. Then, the entire stack of twelve layers (e.g.
61
-
72
) can be clamped and fired at the appropriate temperature and pressure for the required time to form a unitized, monolithic body including an integral window
26
.
In
FIG. 3B
; it is not necessary to join plate
16
′ to plate
30
′ with a separate seal
48
because this joint is made simultaneously with all of the other layers during the cofiring or co-bonding process.
Those skilled in the art will understand that other thicknesses for plates
16
′ and
30
′ can be formed by laminating a different number of layers of the cofired ceramic multilayered material (or co-bonded PWB material). For example, the third example shown in
FIG. 4A
of the present invention illustrates an example where plate
16
′ comprises a fewer number of layers (e.g. two layers:
63
and
64
). In this case, aperture
22
is substantially filled up by window
26
. In this case, window
26
can be fabricated integrally with plate
16
′ by casting molten glass, or by molding a liquid polymer, directly into aperture
22
.
In the example shown in
FIG. 4A
, the size of aperture
22
(and, hence, window
26
) is much smaller than the size of chip or device
100
. It is not required that the size of window
26
be similar to the size of aperture
22
. Also, the example of
FIG. 4A
shows that the centerline of aperture
22
does not align with the centerline of aperture
36
, e.g. aperture
22
is offset from aperture
36
. It is not required that aperture
22
be aligned with aperture
36
. However, aperture
22
can be substantially aligned with aperture
36
. Those skilled in the art will understand that more than one small aperture
22
can be included in plate
16
′, for providing multiple locations for providing optical access to chip or device
100
.
FIG. 4B
shows a schematic cross-section view of a fourth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the second example of
FIG. 3B
, but with window
26
attached to recessed lip
58
formed inside of plate
16
′, wherein the lip can be recessed away from second surface
20
of first plate
16
′. Recessed lip
58
can be easily formed by using a cofired multilayered construction, as described previously.
FIG. 4B
also illustrates that plates
16
′ and
30
′ can extend laterally an unlimited distance beyond the immediate material surrounding apertures
22
and
36
.
Alternatively, the width of plates
16
′ and
30
′ can be limited to extending only a short distance beyond the apertures
22
and
36
, as illustrated in FIG.
4
A. In this example, plates
16
′ and
30
′ can be considered to be a frame for a package that might be housing a single device or chip.
FIG. 4C
shows a schematic cross-section view of a fifth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention that is similar to the second example of
FIG. 3B
, but with window
26
attached flush to second surface
20
of first plate
16
′. Window
26
can be attached to plate
16
′ with seal
38
. Seal
38
can comprise a hermetic sealant material or an adhesive material, as described previously. Alternatively, window
26
can be cofired integrally with plates
16
′ and
30
′.
FIG. 5
shows a schematic cross-section view of a sixth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the first example of
FIG. 3A
; wherein assembly
10
further comprises a second electrically conductive metallized trace
82
disposed on third surface
34
of plate
30
; and a third plate
80
bonded to third surface
34
, wherein plate
80
includes a third aperture
84
through plate
80
; and further wherein at least one lateral dimension of aperture
84
is slightly larger than the corresponding lateral dimension of aperture
36
; and wherein aperture
84
is substantially aligned with aperture
36
. Assembly
10
can further comprise a second bond pad
86
or second electrical lead
88
attached to metallized trace
82
. Assembly
10
can further comprise a second solder-filled via
90
, vertically disposed inside plate
30
. Those skilled in the art will understand that additional plates having apertures and metallized traces can be stacked on top of previous plates, to construct as many levels as is needed.
FIG. 6A
shows a schematic cross-section view of a seventh example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention; further comprising a second package
9
that is substantially identical to the first example of package
8
in
FIG. 3A
, wherein second package
9
can be inverted and bonded with seal
60
to package
8
to form a sealed, symmetric package capable of housing at least two microelectronic devices. In this example, second package
9
serves the function of cover lid
42
(e.g. to cover and seal package
8
).
FIG. 6B
shows a schematic cross-section view of an eighth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention; further comprising a second package
9
that is substantially identical to the first example of package
8
in
FIG. 3A
, wherein second package
9
can be stacked and bonded with seal
60
to package
8
to form a stacked double-package capable of housing at least two microelectronic devices.
FIG. 6C
shows a schematic cross-section view of a ninth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention; further comprising a second package
9
that is substantially identical to the sixth example of package
8
in
FIG. 5
, wherein second package
9
can be inverted and bonded with seal
60
to package
8
to form a sealed, symmetric package capable of housing at least four microelectronic devices. In this example, second package
9
serves the function of cover lid
42
(e.g. to cover and seal package
8
).
FIG. 6D
shows a schematic cross-section view of a tenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention; further comprising a second package
9
that is substantially identical to the sixth example of package
8
in
FIG. 5
, wherein second package
9
can be stacked and bonded with seal
60
to package
8
to form a stacked double-package capable of housing at least four microelectronic devices.
In an eleventh example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the first example of
FIG. 3A
; package
8
further comprises a microelectronic device
100
mounted within assembly
10
. Chip or device
100
can be attached to surface
18
. Chip or device
100
can be flip-chip mounted via interconnect bump
46
to metallized trace
24
. Chip or device
100
can comprise a light-sensitive chip or device (e.g. CCD chip, photocell, laser diode, optical-MEMS, or optical-IMEMS device). Light-sensitive chip or device
100
can be mounted with a light-sensitive side
109
facing towards window
26
. An optional seal
52
can be made between chip or device
100
and first surface
18
of plate
16
, after flip-chip bonding has been performed. Seal
52
can have an annular shape. Seal
52
can provide protection from particulate contamination of the optically active face of chip or device
100
(e.g. active MEMS structures), as well as a second layer of environmental protection in addition to third seal
50
.
In a twelfth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the sixth example of
FIG. 5
; package
8
further comprises a pair of microelectronic devices,
100
and
102
, mounted within assembly
10
. Chip or device
100
can be attached to surface
18
. Chip or device
100
can be flip-chip mounted via interconnect bump
46
to metallized trace
24
. Second chip or device or device
102
can be bonded to the backside of chip or device
100
with bond
104
. Methods for bonding chips or devices back-to-back include anodic bonding, gold-silicon eutectic bonding, brazing, soldering, and polymer-adhesive attachment. Assembly
10
can further comprise a wirebonded electrical lead
106
, electrically attached to metallized trace
82
and to chip or device
102
. Chip or device
102
can include a second light-sensitive side
110
mounted face-up, e.g. facing towards cover lid
42
. Although not illustrated, cover lid
42
can be attached to assembly
10
using a recessed lip similar to the recessed lip
58
shown in FIG.
4
B. Cover lid
42
can be made of a transparent material. Cover lid
42
can also comprise a cofired ceramic multilayered material, which includes a cofired integral window.
In a thirteenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the sixth example of
FIG. 5
; package
8
further comprises a pair of microelectronic devices,
100
and
102
, mounted within assembly
10
. Second chip or device
102
can be flip-chip mounted to metallized trace
82
disposed on surface
32
.
In a fourteenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the ninth example of
FIG. 6A
; package
8
further comprises a pair of microelectronic devices,
100
and
102
, mounted within assembly
10
. In this example, cover lid
42
includes a second window
108
for providing optical access to light-sensitive side
110
of chip or device
102
.
Optional exterior electrical connections
112
can easily be made on the exterior surface of assembly
10
, to provide means for conducting electrical signals between chip or device
100
and chip or device
102
, as needed.
In a fifteenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, that is similar to the ninth example of
FIG. 6C
; package
8
further comprises a first pair of chips or devices, joined to each other back-to-back, and mounted to a first package
8
, and a second pair of chips or devices, joined to each other back-to-back, and mounted to a second package
9
, wherein the second package
9
is inverted and bonded to the first package
8
(as in FIG.
6
C). In this example, a combination of flip-chip and wirebonded interconnects can be used for interconnecting the chips or devices to the four different levels of metallized circuit traces. Also, each of the four chips or devices can comprise optically-active elements, including MEMS structures, thereby providing the possibility of passing an optical signal through both apertures by direct transmission, or by conversion of optical signals to electrical, and back to optical via the optically-active chips or devices. This can be accomplished, in part, by using exterior connections in-between the four different levels of traces
24
.
FIG. 7
shows a schematic top view along line
1
—
1
of
FIG. 3A
of a sixteenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention. Multiple metallized traces can fan out from a smaller pitch to a larger pitch on the periphery of plate
16
. Seals
48
and
52
can have the shape of an annular ring.
FIG. 8
shows a schematic top view of a seventeenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, wherein package
8
can be a multi-chip module (MCM) having a two-dimension array of microelectronic devices. In this example, package
8
includes three compartments having an integral window
26
. These windows can be LTCC or HTCC cofired simultaneously along with the rest of the package. Additional microelectronic devices
116
and microelectronic components
118
(e.g. capacitors, resistors, IC's) can be surface mounted to package
8
by conventional techniques, including flip-chip bonding and wirebonding. Cofired windows
26
and/or cover lids
42
can be placed on either side, or both, of the MCM package
8
. Multiple light-sensitive chips or devices can be mounted inside of the multiple windowed compartments.
FIG. 9
shows a schematic side view of a eighteenth example of a microelectronic package
8
for housing at least one microelectronic device according to the present invention, wherein window
26
further comprises a lens
96
for optically transforming light passing through the window. Lens
96
can be used for focusing or concentrating light onto a smaller, or specified, area on chip or device
100
. Lens
96
can be formed integrally into window
26
, or can be attached separately to the surface of window
26
, as in lens
98
. More than one lens
96
could be integrated with window
26
, with each lens having different optical properties. Alternatively, a divergent lens
96
can be used to spread the light.
Alternatively, the example of
FIG. 9
can comprise an array of binary optic lenslets made integral with the window
26
. Binary optics technology is the application of semiconductor manufacturing methods to the fabrication of optics. A lens or lens array is laid out on a computer CAD program and transferred to a photo-mask using an e-beam or other writing process. A series of photo-masks are used, in conjunction with various etch steps, to build up the structures of interest. This fabrication technique can be used to make arrays of lenses with 1 micron features in completely arbitrary patterns. Lenslet arrays are straightforward to make with these methods, and can be extremely high quality with no dead space between elements. The advantage of binary optics is that the optical fabrication is not limited to spheres and simple surfaces. Lenslet arrays can be effectively used to performing optical remapping, such as transforming a round aperture into a square pupil. More details on the utility and methods for fabricating binary optic lenslet arrays can be found in U.S. Pat. No. 5,493,391 to Neal and Michie; as well as U.S. Pat. No. 5,864,381 by Neal and Mansell. Both of these referenced U.S. Patents are commonly assigned to the present assignee, Sandia Corporation of Albuquerque, N. Mex.
The present invention can also comprise an electrically-switched optical modulator attached to the package. Alternatively, electrically-switched optical modulator can replace window
26
, such as a lithium niobate window. In the example of a lithium niobate window, application of voltages around 5-6 V can switch the material from being transparent to being opaque, at a frequency of a few billion times per second. Such an active window can be used as a very fast shutter to control the amount of light being transmitted through window
26
. More details about use of lithium niobate as a light modulation device can be found in U.S. Pat. No. 5,745,282 to Negi.
The particular examples discussed above are cited to illustrate particular embodiments of the invention. Other applications and embodiments of the apparatus and method of the present invention will become evident to those skilled in the art. For example, the electrically insulating plates with apertures can be replaced with open frames. The actual scope of the invention is defined by the claims appended hereto.
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