U.S. patent application number 11/468709 was filed with the patent office on 2006-12-28 for flexible interconnect structures for electrical devices and light sources incorporating the same.
Invention is credited to Charles Adrian Becker, Thomas Elliot Stecher, Stanton Earl Weaver.
Application Number | 20060292722 11/468709 |
Document ID | / |
Family ID | 28038695 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292722 |
Kind Code |
A1 |
Becker; Charles Adrian ; et
al. |
December 28, 2006 |
FLEXIBLE INTERCONNECT STRUCTURES FOR ELECTRICAL DEVICES AND LIGHT
SOURCES INCORPORATING THE SAME
Abstract
A flexible interconnect structure allows for rapid dissipation
of heat generated from an electrical device that includes
light-emitting elements, such as light-emitting diodes ("LEDs")
and/or laser diodes. The flexible interconnect structure comprises:
(1) at least one flexible dielectric film on which circuit traces
and, optionally, electrical circuit components are formed and at
least a portion of which is removed through its thickness; and (2)
at least a heat sink attached to one surface of the flexible
dielectric film opposite to the surface on which circuit traces are
formed. The flexible interconnect structure can include a plurality
of such flexible dielectric films, each supporting circuit traces
and/or circuit components, and each being attached to another by an
electrically insulating layer. Electrical devices or light sources
having complex shapes are formed from such flexible interconnect
structures and light-emitting elements attached to the heat sinks
so to be in thermal contact therewith.
Inventors: |
Becker; Charles Adrian;
(Schenectady, NY) ; Weaver; Stanton Earl;
(Northville, NY) ; Stecher; Thomas Elliot;
(Scotia, NY) |
Correspondence
Address: |
FAY, SHARPE, FAGAN, MINNICH & MCKEE, LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Family ID: |
28038695 |
Appl. No.: |
11/468709 |
Filed: |
August 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10063104 |
Mar 21, 2002 |
|
|
|
11468709 |
Aug 30, 2006 |
|
|
|
Current U.S.
Class: |
438/28 ; 257/88;
257/E25.02 |
Current CPC
Class: |
H05K 1/021 20130101;
H05K 1/185 20130101; H01L 2924/00 20130101; H01L 25/0753 20130101;
H05K 2201/10106 20130101; H01L 2924/0002 20130101; H01L 33/62
20130101; H05K 2201/10121 20130101; H05K 2201/10416 20130101; H05K
1/189 20130101; H05K 1/0204 20130101; H01L 2924/0002 20130101; H05K
3/4611 20130101; H05K 2201/10219 20130101 |
Class at
Publication: |
438/028 ;
257/088 |
International
Class: |
H01L 21/00 20060101
H01L021/00; H01L 33/00 20060101 H01L033/00 |
Claims
1. A bendable electromagnetic radiation emitting semiconductor dice
array comprising: a plurality of metal heat spreaders; at least one
dielectric layer disposed above a first portion of each of the
underlying plurality of metal heat spreaders, creating a first
portion of a plurality of openings, each opening disposed over a
corresponding metal heat spreader; a bendable electrical
interconnection layer disposed above a first portion of the at
least one dielectric layer and creating a second portion of each
said opening disposed over a corresponding metal heat spreader,
wherein said bendable electrical interconnection layer comprises a
plurality of electrical current pathways; and a plurality of
electromagnetic radiation emitting semiconductor dice, wherein each
of the dice is mounted over a corresponding one of the plurality of
metal heat spreaders with a corresponding thermal conduction means
that provides a direct thermal pathway from the die to the
underlying metal heat spreader, and wherein each die is
electrically coupled to the bendable electrical interconnection
layer.
2. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein said plurality of electromagnetic
radiation emitting semiconductor dice comprises diodes selected
from the group consisting of light emitting diodes (LEDs),
ultraviolet emitting diodes, and laser diodes, and wherein each of
the dice comprises a first electrical contact and a second
electrical contact, said first electrical contact and said second
electrical contact electrically coupled to separate pathways of
said plurality of electrical current pathways.
3. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein each of said thermal conduction
means comprises a thermally conductive adhesive.
4. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein said bendable electrical
interconnection layer comprises a component selected from the group
consisting of bendable printed circuit boards, flexible printed
circuit boards, flex circuits, and metal lead frames.
5. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein said plurality of metal heat
spreaders comprise metal with high thermal conductivity.
6. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein at least one die of said plurality
of electromagnetic radiation emitting semiconductor dice is
thermally coupled to each heat spreader of said plurality of metal
heat spreaders.
7. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein at least one heat spreader of said
plurality of metal heat spreaders comprises an optically reflective
surface disposed to reflect light emitted by at least one die of
said plurality of electromagnetic radiation emitting semiconductor
dice.
8. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein said plurality of metal heat
spreaders are thermally coupled to a heat sink.
9. The bendable electromagnetic radiation emitting
semiconductordice array of claim 1, wherein each heat spreader of
said plurality of metal heat spreaders is structurally coupled to
an adjacent heat spreader of said plurality of metal heat spreaders
via at least one bendable interconnection member disposed
therebetween.
10. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, further comprising at least one optically
transmissive material disposed around at least one die of said
plurality of electromagnetic radiation emitting semiconductor dice
to form at least one housing for said at least one die.
11. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 1, wherein at least one heat spreader of said
plurality of metal heat spreaders comprises an upper portion
elevated above said bendable electrical interconnection layer and
disposed through a corresponding opening of said plurality of
openings, and wherein at least one of the dice of said plurality of
electromagnetic radiation emitting semiconductor dice is disposed
above and thermally coupled to the upper portion of the
corresponding heat spreader.
12. A bendable electromagnetic radiation emitting semiconductor
dice array comprising: a bendable metal frame comprising a
plurality of metal heat spreaders and a plurality of bendable
electrical current pathways; at least one dielectric material
disposed between each heat spreader of said plurality of metal heat
spreaders and at least one pathway of said plurality of bendable
electrical current pathways; and a plurality of electromagnetic
radiation emitting semiconductor dice, wherein each of the dice is
mounted above a portion of the corresponding heat spreader's top
surface with a corresponding thermal conduction means that provides
a direct thermal path from the die to the corresponding heat
spreader, and wherein each of the dice is electrically coupled to
at least two pathways of said plurality of bendable electrical
current pathways; and wherein a heat transfer surface of each heat
spreader of said plurality of metal heat spreaders has a greater
surface area than the bottom surface of each die of said plurality
of electromagnetic radiation emitting semiconductor dice.
13. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 12, wherein at least one heat spreader of said
plurality of metal heat spreaders is thicker than at least one
pathway of said plurality of bendable electrical current pathways,
and wherein each of the dice comprises a first electrical contact
and a second electrical contact, said first electrical contact and
said second electrical contact electrically coupled to separate
pathways of said plurality of bendable electrical current
pathways.
14. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 12, wherein at least one heat spreader of said
plurality of metal heat spreaders comprises a heat spreading region
that widens as the distance from the die mounted above that heat
spreader increases, and wherein each of the dice comprises a first
electrical contact and a second electrical contact, said first
electrical contact and said second electrical contact electrically
coupled to separate pathways of said plurality of bendable
electrical current pathways.
15. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 12, wherein at least one heat spreader of said
plurality of metal heat spreaders is structurally attached to a
corresponding electrical current pathway of said plurality of
bendable electrical current pathways via an electrically conductive
adhesives, and wherein each of the dice comprises a first
electrical contact and a second electrical contact, said first
electrical contact and said second electrical contact electrically
coupled to separate pathways of said plurality of bendable
electrical current pathways.
16. The bendable electromagnetic radiation emitting semiconductor
dice array of claim 12, further comprising a heat sink thermally
coupled to said plurality of metal heat spreaders, and wherein each
of the dice comprises a first electrical contact and a second
electrical contact, said first electrical contact and said second
electrical contact electrically coupled to separate pathways of
said plurality of bendable electrical current pathways.
17. A method of assembling a bendable electromagnetic radiation
emitting semiconductor dice array comprising: providing a bendable
electrical interconnection layer; attaching a plurality of heat
spreaders to the bendable electrical interconnection layer via at
least one adhesive dielectric layer, wherein a portion of a first
surface of each heat spreader is exposed; attaching a plurality of
electromagnetic radiation emitting semiconductor dice to said
plurality of heat spreaders by mounting each die of said plurality
of electromagnetic radiation emitting semiconductor dice to the
exposed portion of the first surface of a corresponding heat
spreader via a corresponding thermal conductor; and electrically
coupling each die of said plurality of electromagnetic radiation
emitting semiconductor dice into a functional electrical circuit
configuration via said bendable electrical interconnection
layer.
18. The method of providing a dice array of claim 17, wherein each
said thermal conductor comprises a thermally conductive
adhesive.
19. The method of providing a dice array of claim 17, wherein said
bendable electrical interconnection layer comprises a component
selected from the group consisting of bendable printed circuit
boards, flexible printed circuit boards, flex circuits, and metal
lead frames.
20. The method of providing a dice array of claim 17, further
comprising the step of bending the bendable electrical
interconnection layer into a 3 dimensional configuration.
21. The method of providing a dice array of claim 17, further
comprising the step of thermally coupling said plurality of heat
spreaders to a heat sink for enhanced heat dissipation.
22. The method of providing a dice array of claim 17, further
comprising the step of providing at least one optically
transmissive material around at least one of the dice to form at
least one housing.
23. A method of providing a bendable electromagnetic radiation
emitting semiconductor dice array comprising: providing a bendable
lead frame structure, wherein said bendable lead frame structure
comprises a plurality of predefined metal heat spreader regions and
a plurality of predefined bendable metal electrical current
pathways; attaching a plurality of electromagnetic radiation
emitting semiconductor dice to said plurality of predefined metal
heat spreader regions by mounting each of the dice to a
corresponding one of the predefined metal heat spreader regions via
a corresponding thermal conductor; and electrically coupling each
die of said plurality of electromagnetic radiation emitting
semiconductor dice into a functional electrical circuit
configuration via at least two pathways of said plurality of
predefined bendable metal electrical current pathways.
24. The method of providing a dice array of claim 23, further
comprising the step of bending said bendable lead frame structure
into a 3 dimensional configuration.
25. The method of providing a dice array of claim 23, further
comprising the step of thermally coupling said plurality of
predefined metal heat spreader regions to a heat sink for enhanced
heat dissipation.
26. The method of providing a dice array of claim 23, further
comprising the step of providing at least one optically
transmissive material around at least one of the dice to form at
least one housing.
Description
[0001] This application claims the benefit of U.S. patent
application Ser. No. 10/063,104, filed Mar. 21, 2002, entitled
"FLEXIBLE INTERCONNECT STRUCTURES FOR ELECTRICAL DEVICES AND LIGHT
SOURCES INCORPORATING THE SAME", the disclosure of which is
incorporated herein in its entirety, by reference.
BACKGROUND OF INVENTION
[0002] The present invention relates to flexible interconnect
structures that support circuits for controlling or operating
electrical devices and light sources incorporating the same. In
particular, the present invention relates to such flexible
interconnect structures and devices that incorporate light-emitting
elements and have improved thermal management capability.
[0003] Light-emitting diodes ("LEDs") are now widely applied in a
variety of signs, message boards, and light sources. The relatively
high efficacy of LEDs (in lumens per watt) is the primary reason
for their popularity. Large power savings are possible when LED
signals are used to replace traditional incandescent signals of
similar luminous output. One aspect of LED technology that has not
been satisfactorily resolved is the efficient management and
removal of waste heat, especially for high optical power LEDs,
requiring increased electrical power. The waste heat results in
excessive junction temperatures, degrading performance and reducing
device life. LED lamps exhibit substantial light output sensitivity
to temperature, and can be permanently degraded by excessive
temperature. For example, the maximum recommended operating
temperature for LEDs that incorporate indium in their compositions
is between about 85.degree. C. and about 100.degree. C. These
devices can exhibit typical (half brightness) lives on the order of
50,000 to 100,000 hours at 25.degree. C. However, degradation above
90.degree. C. is rapid as the LEDs degrade exponentially with
increases in temperature.
[0004] Permanent thermal degradation of LEDs may also occur during
array fabrication if care is not taken, when the LEDs are soldered
to the supporting and/or interconnecting circuit board. For
example, typical soldering temperatures can exceed 250.degree. C.
and seriously affect the performance of the LEDs even before they
are put into service, if the LEDs remain at or near such high
temperatures for an extended period of time. Therefore, it is very
advantageous to remove heat rapidly from the vicinity of LEDs
whether such heat is generated by the LEDs during normal use or
applied during the assembly or manufacturing process.
[0005] One common method for dissipating heat generated from LEDs
that are mounted on an insulating printed circuit board ("PCB"),
such as the commonly available FR-4 fiber composite circuit board,
is to form a plurality of vias under each LED through the thickness
of the PCB. The vias are filled with a metal or alloy having high
thermal conductivity and connected to a heat sink attached to the
PCB opposite to the LED. However, the formation of such vias adds
to the cost of manufacturing the pcb. In addition, the rate of heat
dissipation is limited by the rate of heat conduction through the
vias because of their typical small cross section.
[0006] Another approach is to provide thermally conductive
substrates on which electronic components are mounted. These
substrates generally perform a function of mechanical support, also
provide for electrical interconnection to and between components,
and assist in the extraction and dissipation of heat generated by
the electronic components. These substrates often are costly or
require complicated multi-step manufacturing processes. For
example, substrates have been made of thermally conductive ceramics
or metals coated or laminated with dielectric materials. Thermally
conductive ceramic substrates are costly compared to metals and
are, therefore, more appropriately reserved for high temperature
applications or for devices the price of which is a secondary
concern. When coated or laminated metallic substrates are used, the
electrical insulating property of the coating is important.
Puncture voltage and dielectric dissipation of the insulating
coating directly depend on film thickness, but the rate of heat
dissipation inversely depends on the film thickness. Thus, a
compromise must be accepted which often results in a less efficient
overall device.
[0007] Therefore, there exists a continued need to provide
interconnect structures for LEDs that allow for rapid heat
dissipation and are cost effective and simple to make. In addition,
it is also very desirable to provide interconnect structures for
LEDs that are mechanically flexible such that devices having
substantial curvature are made.
SUMMARY OF INVENTION
[0008] A flexible interconnect structure comprises a flexible
dielectric film having at least a first surface and a second
surface and circuit traces being disposed on at least one of the
film surfaces. In addition, one or more electrical circuit
components can be disposed on a surface of the dielectric film and
connected to at least a circuit trace to form an electrical
circuit. Portions of the flexible dielectric film are removed
through the thickness of the film. Flexible interconnect structures
of the present invention allow for rapid dissipation of heat
generated during the fabrication or use of electrical devices which
comprise such flexible interconnect structures.
[0009] In one aspect of the present invention, an electrical device
comprises: (1) a flexible interconnect structure comprising a
flexible dielectric film having a first surface and a second
surface, electrical circuit components and circuit traces being
disposed on at least one of the film surfaces, at least a portion
of the flexible dielectric film being removed through the thickness
thereof and at least a heat sink attached to one of said film
surfaces, said heat sink covering said portion of said flexible
film that has been removed and being electrically isolated from
said circuit components and at least one of said circuit traces;
and (2) at least one light-emitting diode ("LED") or a laser diode
("LD") attached to said at least a heat sink through said portion
of said flexible film that has been removed such that said LED or
LD is in thermal contact with said heat sink and is electrically
connected to at least one of said circuit traces.
[0010] In another aspect of the present invention, an electrical
device of the present invention is a light source.
[0011] In still another aspect of the present invention, a method
is provided for making a flexible interconnect structure that
allows for a dissipation of heat generated during a fabrication or
use of electrical devices which comprise such flexible interconnect
structures. The method comprises: (1) providing a flexible
dielectric film having a first surface and a second surface; (2)
disposing electrical circuit components and circuit traces on at
least one of said surfaces; and (3) removing at least a portion of
said film through a thickness thereof, said portion being devoid of
said circuit components and said circuit traces.
[0012] In still another aspect of the present invention, the method
further comprises attaching at least a heat sink to one of said
surfaces of said flexible dielectric film, said heat sink covering
said at least a portion of said film that has been removed.
[0013] In still another aspect of the present invention, a method
for making an electrical device comprising at least a LED
comprises: (1) providing a flexible dielectric film having a first
surface and a second surface; (2) disposing electrical circuit
components and circuit traces on at least one of said surfaces; (3)
removing at least a portion of said film through a thickness
thereof, said portion being devoid of said circuit components and
said circuit traces; (4) attaching at least a heat sink to one of
said surfaces of said flexible dielectric film, said heat sink
covering said at least a portion of said film that has been removed
and being electrically isolated from said circuit components and at
least one of said circuit traces; and (5) attaching at least one
LED to said at least a heat sink through said portion of the
flexible film that has been removed such that the LED is in thermal
contact with the heat sink and is electrically connected to at
least one of the circuit traces.
[0014] Other features and advantages of the present invention will
be apparent from a perusal of the following detailed description of
the invention and the accompanying drawings in which the same
numerals refer to like elements.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 shows schematically a section of a flexible
interconnect structure of the present invention.
[0016] FIG. 2 shows the cross-sectional view of the flexible
interconnect structure of FIG. 1 along the cut A-A.
[0017] FIG. 3 illustrates a flexible interconnect of the present
invention that includes multiple layers supporting electrical
circuits.
[0018] FIG. 4 illustrates another embodiment of the multilayer
flexible interconnect of the present invention.
[0019] FIG. 5 shows schematically a flexible interconnect including
heat sinks.
[0020] FIG. 6 shows another embodiment of the flexible interconnect
with heat sinks extending through removed portions of the
dielectric film.
[0021] FIG. 7 shows schematically a LED-based electrical device of
the present invention.
[0022] FIG. 8 shows schematically a flexible interconnect including
heat sinks having fins.
[0023] FIG. 9 shows schematically a flexible interconnect including
heat sinks having heat pipes.
[0024] FIG. 10 shows schematically a flexible interconnect
including heat sinks having cooling coils as an active cooling
mechanism.
DETAILED DESCRIPTION
[0025] As used herein, the term "flexible" means being capable of
being bent to a shape that has a radius of curvature of less than
about 10 cm, and preferably less than about 1 cm. The terms
"electromagnetic radiation" or "light" are used interchangeably.
The term "substantially transparent" means allowing at least 80
percent, preferably at least 90 percent, and more preferably at
least 95 percent of light transmission. The term "heat sink" means
a structure or a component that transports heat away or otherwise
removes heat from a heat source.
[0026] The flexible interconnect structure of the present invention
is equally applicable to devices that include either LEDs, or LDs,
or both. Therefore, although a LED is typically shown or referred
to, a LD may occupy the same position, depending on the design and
purpose of the overall device.
[0027] FIG. 1 shows schematically a section of a flexible
interconnect structure 10 of the present invention. FIG. 2 is a
cross-sectional view of flexible interconnect structure 10 along
the cut A-A. It should be understood that the figures shown herein
are not drawn to scale. Flexible interconnect structure 10
comprises a flexible dielectric film 20 on which electrical circuit
components 30, 32, 34, 36, and 38 and circuit traces 40 are formed
or disposed. Although FIGS. 1 and 2 show only five exemplary
electrical circuit components 30, 32, 34, 36, and 38, any number of
circuit components may be disposed on flexible film 20 as desired.
In fact, current microelectronic fabrication technologies can allow
for the arrangement of hundreds of such components per square
centimeter. Circuit components 30, 32, 34, 36, and 38 may be
resistors, capacitors, inductors, power sources, or even integrated
circuits, each comprising a multitude of other interrelated
electrical or electronic components. Portions 60, 62, and 64 are
removed from flexible dielectric film 20 through the thickness
thereof. Each of these portions 60, 62, and 64 removed from
flexible film 20 is designed to accept a light-emitting element
such as a LED or a LD, or a cup for holding a LED or a LD.
Therefore, the number, shape, and size of these removed portions
depend on the desired application. Typically, a removed portion or
hole 60, 62, or 64 has a diameter of about several millimeters and
is formed in flexible film 20 at predetermined locations where
electrical circuit components and circuit traces are not present.
Holes 60, 62, and 64 are formed into flexible dielectric film by a
method such as laser drilling, laser cutting, mechanical drilling,
punching, or etching.
[0028] Although FIGS. 1 and 2 show flexible interconnect structure
10 comprising only one film, a flexible interconnect structure of
the present invention can comprise a plurality of circuit layers,
each comprising a flexible dielectric film supporting circuit
traces and/or circuit components. FIG. 3 shows the cross-sectional
of an exemplary flexible interconnect structure of the present
invention comprising two circuit layers 22 and 24 separated by an
electrically insulating separation layer 70 disposed therebetween.
In addition, the outermost circuit layer 22 may be desirably
protected with a protective layer 80 of an electrically insulating
material disposed to cover all of the circuit components and
circuit traces, as shown in FIG. 4. The electrical circuits of the
different circuit layers 22 and 24 are typically connected together
by electrically conducting vias such as vias 90 and 92 formed
through the layers at appropriate locations. When a flexible
interconnect structure of the present invention comprises a
plurality of circuit layers, removed portions or holes are formed
through the entire stack of circuit layers.
[0029] Dielectric film 20 typically comprises a polymer having a
high dielectric constant upon which an electrically conductive
material can adhere. The surface of the film on which circuit
components and circuit traces are to be disposed or both of its
surfaces may be desirably cleaned before a next processing step by
exposing such surfaces to a plasma treatment with plasma formed
from a gas selected from the group consisting of N.sub.2, Ar, Ne,
O.sub.2, CO.sub.2, and CF.sub.4. Such a plasma treatment can
advantageously provide the surface of film 20 with a better
adhesion property for deposition of the next layer thereon, which
can be a metallization layer for forming an electrical circuit or a
protective layer of another polymer. Appropriate materials for
dielectric film 20 include; for example, thermoplastic polymers,
acrylic resins, polyester such as Mylar (made by E. I. du Pont de
Nemours & Co.); polyimide such as Kapton H or Kapton E (made by
du Pont), Apical AV (made by Kanegafugi Chemical Industry Company),
Upilex (made by UBE Industries, Ltd.); and polyetherimide such as
Ultem (made by General Electric Company). Suitable dielectric film
materials need to provide electrical isolation so as to prevent
electrical flow across the thickness of the dielectric film.
[0030] Protective layer 80 may be made of a material chosen among
those disclosed above. Protective layer 80 may comprise the same
material as or a different material than that of the flexible film
20. It can be formed by spin coating, spray coating, vacuum
chemical deposition using a mixture of precursors of the polymers
with a solvent followed by curing. Separation layer 70 typically
comprises an organic adhesive such as a siloxane-polyimide-epoxy
(SPIE) or a cyanoacrylate. Separation layer 70 also may be formed
by spin coating, spray coating, or vacuum chemical deposition
followed by curing. A multilayer flexible interconnect structure
may be formed by lamination of different layers together.
Alternatively, the layers may be formed sequentially one on top
another.
[0031] Desirable properties for flexible dielectric film 20 include
an elastic modulus and coefficients of thermal and humidity
expansion that provide minimal dimensional change during
processing. To maintain flexibility, the thickness of flexible
dielectric film 20 is typically minimized. At the same time,
dielectric film 20 must have enough rigidity (due to their
thickness or material composition) to support layers of
metallization on one or both surfaces and maintain dimensional
stability through all subsequent processing steps. Typically, a
thickness of film 20 is in the range from about 1 micrometer to
about 5 mm.
[0032] Electrical circuit components, for example, 30, 32, 34, 36,
and 38 and circuit traces 40 are typically formed on a surface of
dielectric film 20 by microelectronic manufacturing processes. For
example, a metallization layer is first formed on dielectric film
20 by sputtering, dipping, platting, physical vapor deposition,
chemical vapor deposition, or direct bonding or lamination of the
metal. The metallization layer is then patterned by etching using a
photoresist pattern. Alternatively, the circuit components and
circuit traces can be built by depositing appropriate materials
through a mask, such as a photoresist mask. Certain circuit
components such as capacitors and integrated circuits require
deposition of more than one layer, each being patterned with a
separate mask. The interconnect layer may also be formed by direct
printing, screen printing, or pad printing of a conductive ink.
[0033] In one embodiment of the present invention, as shown in FIG.
5, a heat sink 100 is attached to a surface of flexible
interconnect structure 10, which surface is typically opposite to
the surface on which circuit components and circuit traces are
disposed. Each heat sink 100 covers a removed portion or hole (60,
64) formed in the flexible interconnect structure 10 and is
typically attached thereto with an electrically insulating
adhesive, such as an epoxy. Heat sink 100 comprises a thermally
conductive material, such as metals or high-conductivity ceramics;
preferably a metal having high thermal conductivity, such as
silver, aluminum, or copper. The term "high-conductivity ceramic"
means a ceramic having a thermal conductivity greater than about
100 W/m/K. Heat sink 100 may advantageously have a plurality of
fins 102 extending away from the flexible interconnect structure 10
to promote rapid dissipation of heat. Alternatively, heat sink 100
is attached to flexible interconnect structure 10 to cover more
than one removed portion or hole. In still another embodiment, a
sheet of thermally conductive material is attached to flexible
interconnect structure 10 to cover substantially its entire surface
area. These alternative embodiments of heat sinks 100 provide
larger surface areas for heat dissipation by convection.
[0034] In one embodiment of the present invention, heat sink 100
can comprise a mechanism for active cooling. Active cooling can
remove heat faster than cooling that relies on natural convection.
A mechanism for active cooling can include heat pipes 104,
mechanism to effect refrigeration, or mechanism that effects heat
transport by the Peltier effect.
[0035] In another embodiment of the present invention shown in FIG.
6, heat sink 100 has a protrusion 102 extending through a removed
portion or hole 60, 64.
[0036] In still another embodiment of the present invention, as
shown in FIG. 7, an electrical device 200 comprising a flexible
interconnect structure 10 and at least a LED 300. Flexible
interconnect structure 10 comprises a flexible dielectric film 20
having a first surface 16 and a second surface 18, as is disclosed
above. Flexible interconnect structure 10 supports electrical
circuit components such as those shown by numerals 30 and 34 and
circuit traces 40, which can participate in the operation of LED
300. At least a portion (60, 64) of flexible dielectric film 20 is
removed through the thickness thereof. At least a heat sink 100 is
attached to surface 18 of flexible interconnect structure 10 to
cover a removed portion or hole (60, 64) thereof and is
electrically isolated from circuit components 30 and 34 and circuit
traces 40. LED 300 is attached to heat sink 100 and electrically
connected to a circuit that comprises at least some of the circuit
components and circuit traces by conventional methods in the art of
LED packaging, such as soldering or wire bonding. Note that such
electrical connections are not shown in FIG. 7. Typically, LED 300
is disposed in a reflective cup 310 of a reflective metal such as
aluminum and is attached thereto by an electrically insulating,
thermally conductive adhesive. Reflective cup 310 is typically
attached to heat sink 100 with a thin layer of a thermally
conducting adhesive, such as a mixture of an epoxy and metallic
particles; such as copper, silver, or nickel particles. The entire
electrical device 200 may be desirably disposed within a protective
enclosure which comprises an optically transparent cover to allow
light emitted from LED 300 to transmit therethrough and through
which electrical power leads are provided. A wide range of LEDs
emitting electromagnetic ("EM") radiation from the ultraviolet
("UV") to visible range can be used in an electrical device of the
present invention. In one embodiment of the present invention, EM
radiation emitted from LED 300 is converted to EM radiation having
another wavelength by a photoluminescent material disposed in the
vicinity of LED 300. For example, reflective cup 310 can be filled
with a mixture of an optically transparent polymer resin and a
photoluminescent material in particulate form. Alternatively, LED
300 may be painted with such a mixture, and reflective cup 310 is
then filled with an optically transparent polymer resin.
[0037] The flexible interconnect structure of the present invention
with its capability of rapid heat dissipation allows for the
construction of LED-based electrical devices having complex shapes,
such as those having sharp edges or small radii of curvature, that
are not easily constructed with LEDs mounted on rigid printed
circuit boards. For example, a heat sink in the form of a shaped
structure of a thermally conductive material may be wrapped with a
flexible interconnect structure of the present invention, and
light-emitting elements selected from the group consisting of LEDs
and LDs are disposed in contact with the heat sink so as to provide
light in all directions. Such a shaped structure can have a curved
surface or a surface that has sharp corners or edges. In fact, a
flexible interconnect structure of the present invention is very
suitable to be disposed on such shaped structures. Such a shaped
heat sink may be a hollow structure that promotes efficient heat
dissipation. Moreover, a mechanism for active cooling such as one
of the mechanisms disclosed above may be disposed within the cavity
of the hollow heat sink to further enhance the removal of heat from
the light-emitting elements. Efficient heat dissipation with the
design of flexible interconnect structures of the present invention
allows for the application of higher power input to the LEDs
resulting in devices with higher brightness and improved
reliability and in many cases may reduce the total LED count needed
for a system.
[0038] In one aspect of the present invention, a method is provided
for making a LED-based electrical device that has the capability
rapidly to dissipate heat generated by the LED. The method
comprises providing a flexible dielectric film having a first
surface and a second surface; disposing electrical circuit
components and circuit traces on at least one of said surfaces;
removing at least a portion of the dielectric film through its
thickness such that the removed portion does not contain any
circuit components or circuit traces; attaching at least a heat
sink to one of the surfaces of the dielectric film such that the
heat sink substantially covers the removed portion and is
electrically isolated from at least one of the circuit components
and at least one of the circuit traces; and attaching at least a
LED to the heat sink through the removed portion of the dielectric
film such that the LED is in substantial thermal contact with the
heat sink and is electrically connected to at least one of the
circuit traces. The material selection for and the method of
fabricating various elements of the flexible interconnect structure
comprising the circuit components and circuit traces are as
disclosed above.
[0039] In another embodiment of the present invention, the method
for making a LED-based electrical device comprises disposing at
least a LED on a multilayer flexible interconnect structure that
comprises a plurality of layers supporting electrical circuits and
heat sinks covering portions of the flexible interconnect structure
that have been removed to form removed portions or holes through
which at least a LED is attached to the heat sinks. The multilayer
flexible interconnect structure is formed by providing a plurality
of flexible dielectric films, each having two opposed surface;
forming at least a circuit on at least a surface of each of the
flexible dielectric films, each circuit comprising interconnecting
electrical circuit components and circuit traces; attaching the
dielectric films having circuits formed thereon together with
separation layers of electrically insulating materials, each
separation layer being disposed between two of the dielectric
films, the circuits on different dielectric films being connected
together by metallic vias; removing portions of the multilayer
flexible interconnect structure through its thickness to form the
removed portions or holes; attaching heat sinks to an outer surface
of the multilayer flexible interconnect structure; and attaching at
least a LED through a removed portion to a heat sink to make a
thermal contact therewith.
[0040] In still another embodiment of the present invention, the
method comprises the steps of: (a) forming a multilayer stack by:
(1) providing a flexible dielectric film; (2) forming a first
electrical circuit on a surface thereof; (3) depositing a
separation layer of an electrically insulating material on the
electrical circuit; (4) forming a second electrical circuit on the
exposed surface of the separation layer; (5) optionally repeating
steps (3) and (4) as many times as desired to form a multilayer
stack; (b) removing at least a portion of the multilayer stack
through its entire thickness where no electrical components of the
circuits are present to form a removed portion or hole; (c)
attaching a heat sink to an outer surface of the multilayer stack
substantially to cover the removed portion or hole; and (d)
attaching at least a LED to a heat sink to make thermal contact
therewith through a removed portion.
[0041] An electrical circuit of a method of the present invention
can be formed by depositing at least one metallization layer on the
underlying layer, then etching the metallization layer to form
various electrical components. More than one layer may be deposited
one on top of another to form certain electrical components such as
capacitors or integrated circuits. Alternatively, the circuit can
be formed by depositing materials through a mask disposed on the
underlying layer.
[0042] In another aspect of the present invention, the LED is
disposed in a reflective cup that is attached in thermal contact
with the heat sink.
[0043] In still another aspect of the present invention, the
reflective cup is filled with a mixture of a substantially
transparent polymer resin and at least a photoluminescent
material.
[0044] In still another aspect of the present invention, the method
for making a LED-based electrical device of the present invention
further comprises disposing the LED-based electrical device in a
protective enclosure that comprises a substantially transparent
cover disposed in the path of light emitted from the LED. The
LED-based electrical device is used as light sources in
automobiles, traffic signals, message boards, or displays.
[0045] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations, equivalents, or improvements therein may be
made by those skilled in the art, and are still within the scope of
the invention as defined in the appended claims.
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