U.S. patent application number 13/886878 was filed with the patent office on 2018-03-22 for light emitting diode component.
The applicant listed for this patent is Srinath K. Aanegola, Matthew Mrakovich, Emil V. Radkov, James Reginelli, Thomas F. Soules, Larry R. Stadelman, Tomislav J. Stimac, Stanton Earl Weaver, JR.. Invention is credited to Srinath K. Aanegola, Matthew Mrakovich, Emil V. Radkov, James Reginelli, Thomas F. Soules, Larry R. Stadelman, Tomislav J. Stimac, Stanton Earl Weaver, JR..
Application Number | 20180080614 13/886878 |
Document ID | / |
Family ID | 51841336 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180080614 |
Kind Code |
A9 |
Aanegola; Srinath K. ; et
al. |
March 22, 2018 |
LIGHT EMITTING DIODE COMPONENT
Abstract
In a lighting package, a printed circuit board supports at least
one light emitting die. A light transmissive cover is disposed over
the at least one light emitting die. A phosphor is disposed on or
inside of the light transmissive dome-shaped cover. The phosphor
outputs converted light responsive to irradiation by the at least
one light emitting die. An encapsulant substantially fills an
interior volume defined by the light-transmissive cover and the
printed circuit board.
Inventors: |
Aanegola; Srinath K.; (Parma
Heights, OH) ; Radkov; Emil V.; (Euclid, OH) ;
Reginelli; James; (North Royalton, OH) ; Stadelman;
Larry R.; (Stow, OH) ; Mrakovich; Matthew;
(Streetsboro, OH) ; Stimac; Tomislav J.; (Concord,
OH) ; Weaver, JR.; Stanton Earl; (Northville, NY)
; Soules; Thomas F.; (Livermore, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aanegola; Srinath K.
Radkov; Emil V.
Reginelli; James
Stadelman; Larry R.
Mrakovich; Matthew
Stimac; Tomislav J.
Weaver, JR.; Stanton Earl
Soules; Thomas F. |
Parma Heights
Euclid
North Royalton
Stow
Streetsboro
Concord
Northville
Livermore |
OH
OH
OH
OH
OH
OH
NY
CA |
US
US
US
US
US
US
US
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140328046 A1 |
November 6, 2014 |
|
|
Family ID: |
51841336 |
Appl. No.: |
13/886878 |
Filed: |
May 3, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12884717 |
Sep 17, 2010 |
8436380 |
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13886878 |
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11312268 |
Dec 20, 2005 |
7800121 |
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12884717 |
|
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10831862 |
Apr 26, 2004 |
7224000 |
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11312268 |
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PCT/US2003/027363 |
Aug 29, 2003 |
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10831862 |
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10909564 |
Aug 2, 2004 |
7768189 |
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12884717 |
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60407426 |
Aug 30, 2002 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/505 20130101;
H01L 2224/48091 20130101; H01L 33/58 20130101; F21Y 2115/10
20160801; F21V 13/08 20130101; H01L 2924/181 20130101; F21Y 2105/10
20160801; F21K 9/64 20160801; H01L 2224/48227 20130101; H01L 33/508
20130101; H01L 33/507 20130101; F21K 9/68 20160801; H01L 33/46
20130101; H01L 33/60 20130101; H01L 2224/48091 20130101; H01L
2924/00014 20130101; H01L 2924/181 20130101; H01L 2924/00012
20130101 |
International
Class: |
F21K 99/00 20060101
F21K099/00; F21V 13/08 20060101 F21V013/08 |
Claims
1-63. (canceled)
64. A lighting apparatus comprising: at least one light emitting
diode (LED) chip; and at least one luminescent element comprising
at least one phosphor, the luminescent element spaced from the LED
chip by a distance at least 2 times the length of the LED chip, the
luminescent element having a phosphor coated surface area at least
10 times as large as the exposed surface area of light absorbing
components of the LED chip.
65. The lighting apparatus according to claim 64, wherein the
phosphor performs wavelength conversion of light emitted by the LED
chip.
66. The lighting apparatus according to claim 64, further
including: a common reflective support on which both the LED chip
and the luminescent element are mounted.
67. The lighting apparatus according to claim 66, wherein the
luminescent element is a hemispheric shape, and wherein the LED
chip is sealed between the common reflective surface and the
luminescent element.
68. The lighting apparatus according to claim 67, wherein the LED
chip is disposed at the center of the luminescent element.
69. The lighting apparatus according to claim 66, further
including: a submount or substrate of the LED chip, the submount or
substrate mounted on the common reflective support and disposed
between the common reflective support and the LED chip.
70. The lighting apparatus according to claim 66, wherein the
common reflective support is planar.
71. The lighting apparatus according to claim 66, wherein the
common reflective support includes a heat sink for the LED
chip.
72. The lighting apparatus according to claim 66, wherein the
common reflective support comprises a reflector cup including
sidewalls, the LED chip disposed in the reflector cup.
73. A lighting apparatus comprising: at least one light emitting
diode (LED) chip; at least one luminescent element comprising at
least one phosphor, the luminescent element having a phosphor
coated surface area at least 10 times as large as the exposed
surface area of light absorbing components of the LED chip; and a
common reflective support on which both the LED chip and the
luminescent element are mounted, the LED chip sealed between the
common reflective surface and the luminescent element.
74. The lighting apparatus according to claim 73, wherein the
phosphor performs wavelength conversion of light emitted by the LED
chip.
75. The lighting apparatus according to claim 73, wherein the
luminescent element is a hemispheric shape, the LED chip disposed
at the center of the luminescent element.
76. The lighting apparatus according to claim 73, further
including: a submount or substrate of the LED chip, the submount or
substrate mounted on the common reflective support and disposed
between the common reflective support and the LED chip, wherein the
LED chip is disposed on the submount or substrate.
77. The lighting apparatus according to claim 73, wherein the
common reflective support is planar.
78. The lighting apparatus according to claim 73, wherein the
common reflective support includes a heat sink for the LED
chip.
79. The lighting apparatus according to claim 73, wherein the
common reflective support comprises a reflector cup including
sidewalls, the LED chip being disposed in the reflector cup.
80. A lighting apparatus comprising: a light source selected from a
group consisting of (i) a single light emitting diode (LED) chip
and (ii) a plurality of LED chips facing a same direction; a
spherical surface spaced apart from and surrounding the light
source, the spherical surface comprising phosphor configured to
perform wavelength conversion of light emitted by the light source;
a common reflective support on which both the light source and a
hemisphere of the a spherical surface are mounted; and a submount
or substrate of the light source, the submount or substrate mounted
on the common reflective support and disposed between the common
reflective support and the light source.
81. The lighting apparatus according to claim 80, wherein the
spherical surface is spaced from the light source by a distance at
least 2 times the length of an LED chip.
82. The lighting apparatus according to claim 80, wherein the
spherical surface includes a phosphor coated surface area at least
10 times as large as the exposed surface area of light absorbing
components of the light source.
83. The lighting apparatus according to claim 80, wherein the
common reflective support is planar.
Description
[0001] This application is a continuation of application Ser. No.
11/312,268 filed Dec. 20, 2005 which is a continuation-in-part of
application Ser. No. 10/831,862 filed Apr. 26, 2004 and since
issued as U.S. Pat. No. 7,224,000 which is a continuation-in-part
of International Application number PCT/US2003/027363 with an
international filing date of Aug. 29, 2003 first published Mar. 11,
2004 as International Publication no. WO 2004/021461 A2, which
claims the benefit of U.S. Provisional Application Ser. No.
60/407,426 filed on Aug. 30, 2001 This application is also a
continuation-in-part of application Ser. No. 10/909,564 filed Nov.
2, 2004 and since issued as U.S. Pat. No. 7,768,189.
[0002] This application incorporates by reference the content of
application Ser. No. 11/312,268, which has published as US
2006-0097245 A1. This application incorporates by reference the
content of application Ser. No. 10/831,862, which has issued as
U.S. Pat. No. 7,224,000 and has published as US 2005-0239227 A1.
This application incorporates by reference the content of
International Application number PCT/US2003/027363. This
application incorporates by reference the content of U.S.
Provisional Application Ser. No. 60/407,426. This application
incorporates by reference the content of application Ser. No.
10/909,564, which has published as US 2006-0022582 A1 and has
issued as U.S. Pat. No. 7,768,189.
BACKGROUND
[0003] The present invention relates to the lighting arts. It
especially relates to single-chip and multiple-chip light emitting
diode components and methods for making same, and will be described
with particular reference thereto. However, the invention applies
to light emitting packages generally, and is applicable in
packaging monolithic light emitting diode array dice, edge-emitting
laser dice, vertical cavity light emitting dice or monolithic laser
array dice, organic light emitting devices or organic light
emitting array devices, and the like. The inventive light emitting
packages and components will find application in substantially any
application that employs one or more light sources.
[0004] Light emitting diode components provide illumination in
small, rugged, reliable packages. Light emitting diodes have been
developed in many colors spanning the visible spectrum and
extending into the infrared and ultraviolet. While each light
emitting diode typically emits light in a narrow spectral range,
primary color light emitting diodes can be combined to emit white
light. In another approach for generating white light, light from a
blue, violet, or ultraviolet light emitting diode is coupled with a
suitable phosphor to produce white light. Other colors can
similarly be generated by suitable selection of light emitting die
components, phosphors, and combinations of die components and
phosphors.
[0005] One issue with light emitting diode components or packages
relates to light output intensity. Early light emitting diodes had
low light output intensities and were generally not competitive
with incandescent and fluorescent light sources. Improvements in
crystal growth, device fabrication, packaging methods, phosphor
materials, and the like have substantially improved the light
output intensities of modern light emitting diode packages.
However, improvements in light output intensities are still being
sought.
[0006] Another issue with light emitting diode components and
packages relates to ruggedness. Commonly used packaging techniques,
such as bonding of the dice to lead frames, can produce relatively
fragile light emitting packages. Moreover, light emitting diode
components and packages tend to be complex. A typical single-chip
package may include, for example, a light emitting diode die, a
lead frame, an encapsulant disposed over the light emitting diode
die and a portion of the lead frame, and a phosphor embedded in the
encapsulant.
[0007] Multiple chip packages generally further increase
complexity. One example of such a multiple chip package is
disclosed in Lowery, U.S. Pat. No. 6,504,301, which shows various
arrangements involving generally wire-bonded interconnection of a
plurality of light emitting dice disposed on a support placed in a
housing including a cylindrical casing and a fluorescent plate. A
similar multiple chip package is disclosed in Baretz et al., U.S.
Pat. No. 6,600,175. Baretz discloses a phosphor contained in an
encapsulant disposed inside the housing. The complexity of multiple
chip packages such as those of Lowery and Baretz can adversely
impact manufacturability, reliability, and manufacturing costs.
[0008] Another issue with typical light emitting diode packages and
components is operating lifetime. Performance of packages employing
phosphor wavelength conversion of ultraviolet or short-wavelength
visible light typically degrades over time due to discoloration or
other degradation of the encapsulant or other materials caused by
the ultraviolet or short-wavelength visible light irradiation.
[0009] Another issue with typical light emitting diode packages is
plug-in capability with lighting fixtures. A typical light emitting
diode package is configured as a discrete electronic component and
includes a lead frame or other electronic component mounting
arrangement designed for solder connection. This approach is
suitable for applications such as visual power indicators. For
illumination, however, the light emitting diode package would
desirably be used in a manner more analogous to a light bulb,
fluorescent lighting tube, halogen bulb, or so forth, rather than
as a discrete electronic component. To enable plug-in capability,
the light emitting diode package for illumination applications
should be readily connectable with existing illumination fixtures
such as Edison sockets, track lighting fixtures, or so forth. Such
plug-in fixture compatibility is, however, hampered by the
typically high voltage and/or high frequency electrical power
supplied by such fixtures, which is not conducive to powering
low-voltage light emitting diode devices.
[0010] Another issue with using light emitting diode packages for
illumination is light output quality. When light emitting diode
packages employ several light emitting chips so as to produce high
light intensity, a problem arises in that the output consists of
several approximate point light sources corresponding to the
several chips. This pixelated spatial distribution of light is
problematic for illumination applications.
[0011] Spectral light output quality can also be an issue when
using light emitting diode packages for white illumination. For
example, different applications may call for different color
rendering index (CRI) values. Obtaining white light or
substantially white light with a desired (usually high) CRI value
in a commercially practical manner is difficult. Existing
cost-effective "white" phosphor compositions sometimes have
relatively low CRI values.
[0012] The present invention contemplates improved apparatuses and
methods that overcome the above-mentioned limitations and
others.
BRIEF SUMMARY
[0013] According to one aspect, a light emitting package is
disclosed. A printed circuit board supports at least one light
emitting die and has at least two electrical terminals. Printed
circuitry of the printed circuit board connects the at least one
light emitting die with the at least two electrical terminals to
provide power thereto. A light transmissive cover is disposed over
the at least one light emitting die but not over the at least two
electrical terminals. The cover has an open end defining a cover
perimeter connected with the printed circuit board. An inside
surface of the cover together with the printed circuit board
defines an interior volume containing the at least one light
emitting die. An encapsulant is disposed in the interior volume and
covers at least the light emitting die.
[0014] According to another aspect, a light emitting package is
disclosed. A support has at least one light emitting die disposed
thereon. A glass cover is disposed on the support over the at least
one light emitting die. The glass cover and the support
cooperatively define an interior volume containing the at least one
light emitting die. An encapsulant is disposed in the interior
volume and encapsulates the at least one light emitting die.
[0015] According to another aspect, a light emitting package is
disclosed. A support has at least one light emitting die disposed
thereon. A single piece light transmissive cover is disposed on the
support over the at least one light emitting die. The single piece
cover and the support cooperatively define a substantially closed
interior volume containing the at least one light emitting die. An
encapsulant is disposed in the interior volume and encapsulates the
at least one light emitting die.
[0016] According to another aspect, a method is provided for making
a light emitting package. At least one light emitting die is
electrically and mechanically connected to a printed circuit board.
A light transmissive cover is secured to the printed circuit board.
The light transmissive cover covers the at least one light emitting
die. The secured light transmissive cover and the printed circuit
board cooperatively define an interior volume. An encapsulant is
disposed in the interior volume.
[0017] According to another aspect, a method is provided for
disposing of a phosphor on a surface. An adhesive is disposed on
the surface. A phosphor powder is applied to the adhesive. The
adhesive is hardened.
[0018] According to another aspect, a lighting package is
disclosed. A printed circuit board supports at least one light
emitting die. A light transmissive cover is disposed over the at
least one light emitting die. At least one phosphor composition
comprising at least one phosphor compound is disposed on or inside
of the light transmissive cover. The at least one phosphor
composition outputs converted light responsive to irradiation by
the at least one light emitting die.
[0019] According to another aspect, a lighting package is
disclosed. A printed circuit board supports at least one light
emitting die. A light transmissive cover is disposed over the at
least one light emitting die. An encapsulant substantially fills an
interior volume defined by the light-transmissive cover and the
printed circuit board.
[0020] According to another aspect, a lighting package is
disclosed. A printed circuit board supports at least one light
emitting die. A light transmissive cover is disposed over the at
least one light emitting die. Electrical power-conditioning
circuitry is disposed on the printed circuit board and is
configured to condition received input power to energize the
supported at least one light emitting die.
[0021] Numerous advantages and benefits of the present invention
will become apparent to those of ordinary skill in the art upon
reading and understanding the present specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention may take form in various components and
arrangements of components, and in various process operations and
arrangements of process operations. The drawings are only for
purposes of illustrating preferred embodiments and are not to be
construed as limiting the invention.
[0023] FIG. 1 shows a perspective view of a lighting component or
package.
[0024] FIG. 2 shows a perspective view of the printed circuit board
of the lighting package of FIG. 1 with the light emitting dice or
chips and associated electrical components disposed thereon.
[0025] FIG. 3 shows a perspective view of the lighting component or
package of FIG. 1 with a portion of the light transmissive cover
removed to show internal elements of the lighting package.
[0026] FIG. 4 diagrams an example process for manufacturing the
lighting package of FIG. 1.
[0027] FIG. 5 shows a perspective view of another lighting
component or package having backside electrical terminals.
[0028] FIG. 6 shows CRI tuning using a first phosphor composition
having phosphor compounds (A,B,C) and a second phosphor composition
having phosphor compounds (B,C,D).
[0029] FIG. 7 shows a high CRI spectrum achievable using the CRI
tuning of FIG. 6.
[0030] FIG. 8 shows a perspective view of another lighting
component or package having light emitting chips arranged in a long
double-row. In FIG. 8, a portion of the light transmissive cover is
removed to show some of the light emitting dice or chips and other
internal components.
[0031] FIG. 9 shows a perspective view of another lighting
component or package, in which the light emitting dice and the
phosphor are encapsulated by separate encapsulants. In FIG. 9, a
portion of the light transmissive cover removed to show internal
elements of the lighting package.
[0032] FIG. 10 diagrams an example process for manufacturing the
lighting package of FIG. 9.
[0033] FIG. 11 shows a perspective view of another lighting
component or package, in which the printed circuit board includes
two evaporated conductive traces. In FIG. 11, a portion of the
light transmissive cover removed to show internal elements of the
lighting package.
[0034] FIG. 12 shows a perspective view of another lighting
component or package having light emitting chips arranged in a
double-row, with a plurality of dome-shaped light-transmissive
covers disposed over the light emitting chips.
[0035] FIG. 13 shows a side sectional view of another lighting
component or package having a light transmissive dome-shaped cover
on which two different phosphor layers are disposed.
[0036] FIG. 14 is an enlarged sectional view of a portion of the
light transmissive dome-shaped cover of FIG. 13, showing an
optional ultraviolet reflective coating is disposed between the
dome-shaped cover and the phosphor layers.
[0037] FIG. 15 shows a side sectional view of another lighting
component or package having a light transmissive non-dome-shaped
cover on which two different phosphor layers are disposed.
[0038] FIG. 16 shows a perspective view of another lighting
component or package similar to that of FIGS. 1-3, but having the
phosphor compositions screen-printed to display a corporate name
and logo.
[0039] FIG. 17 is perspective view of a conventional LED package
assembly.
[0040] FIG. 18 is a cross-sectional view of an LED assembly.
[0041] FIG. 19 is a cross-sectional view of an LED assembly.
[0042] FIG. 20 is a cross-sectional view of an LED assembly.
[0043] FIG. 21 is a cross-sectional view of an LED assembly.
[0044] FIG. 22 is a side perspective view of an LED assembly.
[0045] FIG. 23 is a side perspective view of an LED assembly.
[0046] FIG. 24 is a representation of an LED assembly according to
an embodiment depicting flux lines for radiation incident on its
various surfaces.
[0047] FIG. 25 is a cross-sectional view of a lens for a blue LED
source containing a band pass filter.
[0048] FIG. 26 is a cross-sectional view of a lens for a UV LED
containing multiple band pass filters.
[0049] FIG. 27 is a cross-sectional view of a lens containing an
array of micro or macro lenses is formed on the outer surface of
the lens to control the emission angle, direction or intensity of
the emitted radiation.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] With reference to FIGS. 1-3, a light emitting package 8
includes a printed circuit board 10 on which one or more light
emitting chips or die are disposed. The printed circuit board is
preferably substantially thermally conductive. For example, a metal
core printed circuit board can be employed. In the illustrated
embodiment, three light emitting chips or dice 12, 14, 16 are
disposed on the circuit board 10; however, the number of dice can
be one die, two dice, or more than three dice. The die or dice can
be group III-nitride blue or ultraviolet light emitting diodes, red
group III-phosphide or group III-arsenide light emitting diodes,
II-VI light emitting diodes, IV-VI light emitting diodes, silicon
or silicon-germanium light emitting diodes, or the like. As used
herein, the term "ultraviolet" is intended to encompass light
emitting diode emission having a peak wavelength less than or about
425 nm. In some contemplated embodiments, the die or dice are edge
emitting lasers or vertical cavity surface emitting lasers. The
light emitting chips or dice can also be organic light emitting
diodes or devices. Each light emitting die or dice can be a bare
die, or each die or dice can include an individual encapsulant.
Still further, the die or dice can be a monolithic array of light
emitting diode mesas, vertical cavity surface emitting laser mesas,
or the like. In the illustrated embodiment, the dice 12, 14, 16 are
disposed in corresponding reflective wells 22, 24, 26; however, the
die or dice may be mounted on a planar surface of the printed
circuit board 10 or can be mounted on raised pedestals or other
elevated support structures. In some embodiments, a portion or all
of the side of the printed circuit board 10 on which the light
emitting dice or chips 12, 14, 16 are disposed has a reflective
layer disposed thereon to improve light extraction from the package
8.
[0051] With particular reference to FIG. 3, the illustrated printed
circuit board 10 includes one or more printed circuitry layers 30
sandwiched between insulative layers 32, 34. Typically, electrical
pads are formed on the die attach surface of the printed circuit
board 10 using appropriate vias passing through the insulative
layer 32 to electrically connect the dice 12, 14, 16 with the
printed circuitry 30. The die or dice 12, 14, 16 can be
mechanically and electrically attached to the printed circuit board
10 in various ways, such as: by flip-chip bonding of die electrodes
to electrical pads of the printed circuit board 10; by soldering
the die to the board 10 and using wire bonds to electrically
connect the die electrodes with electrical pads of the printed
circuit board 10; by soldering the die to a lead frame (not shown)
that is in turn mounted to the printed circuit board 10; or so
forth. The die attachment can include a sub-mount (not shown)
disposed between a light emitting die or chip and the printed
circuit board or other support, or between the chip and a lead
frame. In some embodiments, chip bonding is achieved using
thermosonic bonding, thermocompressive bonding, ultrasonic bonding,
eutectic bonding with or without underfill, or so forth. Still
further, rather than mounting individual dice as illustrated
herein, it is contemplated to employ a monolithic light emitting
diode array formed on a common substrate. In this contemplated
embodiment, the common substrate is soldered, thermosonically
bonded, thermocompressively bonded, or otherwise secured to the
printed circuit board 10, and electrical connection to the
individual light emitting mesas or structures is made by wire
bonding, conductive traces formed on the common substrate, or the
like. Alternatively, a monolithic array having a transparent common
substrate can be configured for a flip-chip mounting in which the
electrodes of the light emitting mesas or structures are directly
bonded to electrical pads.
[0052] The printed circuit board 10 preferably further includes a
heat sinking structure such as a ground plate or metal core 38 to
provide heat sinking of the light emitting chips or dice 12, 14,
16. Optionally, an insulative back-plate (not shown) is disposed on
the side of the metal core 38 distal from the die attach surface.
The heat sink is optionally omitted in lower power lighting
packages, packages mounted on a heat sinking surface, or the like.
Moreover, the printed circuitry layer or layers 30 may provide
adequate heat sinking in some embodiments. In still yet other
embodiments, the material or materials forming the insulative
layers 32, 34 are chosen to be thermally conductive so that these
layers provide heat sinking
[0053] The printed circuit board 10 optionally supports associated
electrical components, such as a zener diode component 44 including
one or more zener diodes connected across the light emitting dice
12, 14, 16 by the printed circuitry 30 to provide electrostatic
discharge protection for the dice. Similarly, electrical power
conversion circuitry, power regulating circuitry, voltage
stabilizing circuitry, current-limiting circuitry, rectifying
circuitry, various combinations thereof, or the like, can be
included as additional components on the printed circuit board 10.
Such components can be provided as one or more discrete components,
or as an application-specific integrated circuit (ASIC). Moreover,
an electrical plug, adaptor, electrical terminals 46, or the like
can be disposed on the printed circuit board 10. In some
embodiments, it is contemplated to include more than one set of
electrical terminals, for example to enable series, parallel, or
series-parallel interconnection of a plurality of light emitting
packages. The printed circuitry 30 includes traces connecting the
electrical terminals 46 with the light emitting dice or chips 12,
14, 16 such that suitable electrical power applied to the
electrical terminals 46 energizes the light emitting dice or chips
12, 14, 16 and associated circuitry (if any) such as the zener
diode component 44, voltage stabilizing circuitry, current limiting
circuitry, or so forth. The printed circuit board 10 can include
other features such as a mounting socket, mounting openings 50, 52
or the like for mechanically installing or securing the light
emitting package 8.
[0054] The described printed circuit board 10 is an example. Other
types of printed circuit boards or other support structures can
also be employed. For example, the printed circuit traces can be
disposed on the die attach surface and/or on the bottom surface
rather than being sandwiched between insulative layers 32, 34.
Thus, for example, the printed circuit board can be an electrically
insulating support with a conductive trace evaporated and patterned
or otherwise formed on the insulating support. Moreover, a heat
sink can be substituted for the printed circuit board, for example
with the light emitting die or dice soldered or otherwise
mechanically secured to the heat sink and with the die electrodes
wire bonded to electrical pads.
[0055] With continuing reference to FIGS. 1-3, the light emitting
package further includes a light transmissive cover 60 disposed
over the light emitting dice or chips 12, 14, 16. The light
transmissive cover has an open end defining a cover perimeter 62
that connects with the printed circuit board 10. In the illustrated
embodiment, the printed circuit board 10 includes an optional
annular groove 66 that receives the perimeter 62 of the light
transmissive cover 60, which in the light emitting package 8 is a
hemispherical dome-shaped cover. The groove 66 guides in
positioning the cover 60 on the printed circuit board 10, and
optionally also is used to help secure the cover to the board. In
some embodiments the annular groove 66 is omitted, in which case
the placement of the cover 60 on the printed circuit board 10 is
positioned by other means, such as by using an automated assembly
jig.
[0056] The light transmissive cover 60 can be secured to the
printed circuit board 10 in various ways, such as by an adhesive,
by a friction fit between the perimeter 62 and the groove 66, by
fasteners, or so forth. The light transmissive cover 60 together
with the printed circuit board 10 define an interior volume 70
containing the light emitting dice or chips 12, 14, 16. In some
embodiments, the connection between the perimeter 62 of the light
transmissive cover 60 and the printed circuit board 10 is a
substantially airtight sealing connection that substantially
hermetically seals the interior volume 70. In other embodiments,
the connection between the perimeter 62 and the printed circuit
board 10 is not a hermetic seal, but rather may contain one or more
gaps, openings, or the like.
[0057] A phosphor 72 (indicated by a dotted line in FIG. 3) is
optionally disposed on an inside surface of the cover 60. If
provided, the phosphor is selected to produce a desired wavelength
conversion of a portion or substantially all of the light produced
by the light emitting dice or chips 12, 14, 16. The term "phosphor"
is to be understood as including a single phosphor compound or a
phosphor blend or composition of two or more phosphor compounds
chosen to produce a selected wavelength conversion. For example,
the phosphor 72 may be a phosphor composition including red, green,
and blue phosphor compounds that cooperatively provide white or
substantially white light. In some embodiments, the tri-phosphor
blend of (Ba,Sr,Ca).sub.5(PO.sub.4).sub.3Cl:Eu.sup.2+,
Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+, and
3.5MgO*0.5MgF.sub.2*GeO.sub.2:Mn.sup.4+ phosphors is used. In some
embodiments, the phosphor compound
(Ca,Sr,Ba).sub.2Si.sub.1-cO.sub.4-2c:Eu.sup.2+ where
0.ltoreq.c<0.25 is used alone or in combination with other
phosphor compounds, and the phosphor is excited by a light emitting
diode die or chip emitting radiation having a peak emission from
about 200 nm to about 500 nm. In some embodiments, the phosphor
composition includes phosphor compounds
(Ca,Sr,Ba)Al.sub.2O.sub.4:Eu.sup.2+,
Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+, and
(Ca,Sr,Ba)MgAl.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+. For purposes of
the present application, it should be understood that when a
phosphor has two or more dopant ions (i.e. those ions following the
colon in the above compositions), this is meant to mean that the
phosphor has at least one (but not necessarily all) of those dopant
ions within the material. That is, as understood by those skilled
in the art, this type of notation means that the phosphor can
include any or all of those specified ions as dopants in the
formulation. In some embodiments, the phosphor blend is selected to
provide white light with color coordinates lying on or near the
blackbody locus and a color temperature less than 4500K. In some
embodiments, the phosphor blend is selected to provide white light
with color coordinates lying on or near the blackbody locus and a
color rendering index (R.sub.a) of 90 or greater.
[0058] Some various suitable phosphor compounds that can be used
alone as a single-compound phosphor composition and/or in
combination with other phosphor compounds as a multiple-compound
phosphor composition are listed here: [0059]
(Mg,Ca,Sr,Ba,Zn).sub.5(PO.sub.4).sub.3Cl:Eu.sup.2+ [0060]
(Ca,Sr,Ba).sub.2Si.sub.1-cO.sub.4-2c:Eu.sup.2+ where
0.ltoreq.c<0.25 [0061]
(Ba,Sr,Ca).sub.5(PO.sub.4).sub.3(Cl,F,Br,OH):Sb.sup.3+,Mn.sup.2+
[0062] (Mg,Ca,Sr,Ba,Zn).sub.5(PO.sub.4).sub.3(F,Cl,
Br,OH):Eu.sup.2+,Mn.sup.2+ [0063]
(Ba,Sr,Ca)BPO.sub.5:Eu.sup.2+,Mn.sup.2+ [0064]
(Sr,Ca).sub.10(PO.sub.4).sub.6*nB.sub.2O.sub.3:Eu.sup.2+ [0065]
Sr.sub.2Si.sub.3O.sub.8*2SrCl.sub.2:Eu.sup.2+ [0066]
Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+ [0067]
(Ca,Sr,Ba)MgAl.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+ [0068]
Ba.sub.3MgSi.sub.2O.sub.8:Eu.sup.2+ [0069]
BaAl.sub.8O.sub.13:Eu.sup.2+ [0070]
2SrO*0.84P.sub.2O.sub.5*0.16B.sub.2O.sub.3:Eu.sup.2+; [0071]
(Ba,Sr,Ca)Al.sub.2O.sub.4:Eu.sup.2+ [0072]
(Y,Gd,Lu,Sc,La)BO.sub.3:Ce.sup.3+,Tb.sup.3+ [0073]
Ca.sub.8Mg(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+,Mn.sup.2+ [0074]
(Ba,Sr,Ca).sub.2(Mg,Zn)Si.sub.2O.sub.7:Eu.sup.2+ [0075]
(Sr,Ca,Ba)(Al,Ga,In).sub.2S.sub.4:Eu.sup.2+ [0076]
(Y,Gd,Tb,La,Sm,Pr,Lu).sub.3(Al,Ga).sub.5-fO.sub.12-3/2f:Ce.sup.3+
(wherein 0.ltoreq.f.ltoreq.0.5) [0077]
(Lu,Y,Sc).sub.2-g(Ca,Mg).sub.1+gLi.sub.hMg.sub.2-h(Si,Ge).sub.3-hP.sub.hO-
.sub.12-g:Ce.sup.3+ (wherein 0.ltoreq.g.ltoreq.0.5,
0.ltoreq.h.ltoreq.0.5) [0078]
(Ca,Sr).sub.8(Mg,Zn)(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+,Mn.sup.2+
[0079] Na.sub.2Gd.sub.2B.sub.2O.sub.7:Ce.sup.3+, Tb.sup.3+ [0080]
(Sr,Ca,Ba,Mg,Zn).sub.2P.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+ [0081]
(Ca,Sr,Ba,Mg,
Zn).sub.10(PO.sub.4).sub.6(F,Cl,Br,OH).sub.2:Eu.sup.2+,Mn.sup.2+
[0082] (Gd,Y,Lu,La).sub.2O.sub.3:Eu.sup.3+,Bi.sup.3+ [0083]
(Gd,Y,Lu,La).sub.2O.sub.2S:Eu.sup.3+,Bi.sup.3+ [0084]
(Gd,Y,Lu,La)VO.sub.4:Eu.sup.3+,Bi.sup.3+ [0085]
SrY.sub.2S.sub.4:Eu.sup.2+ [0086] CaLa.sub.2S.sub.4:Ce.sup.3+
[0087] (Ca,Sr)S:Eu.sup.2+ [0088]
(Ba,Sr,Ca)MgP.sub.2O.sub.7:Eu.sup.2+,Mn.sup.2+ [0089]
(Y,Lu).sub.2WO.sub.6:Eu.sup.3+,Mo.sup.6+ [0090]
(Ba,Sr,Ca).sub.uSi.sub.v(N,O).sub.w:Eu.sup.2+ [0091]
(Lu,Ca,Li,Mg,Y)alpha-SiAlON doped with Eu.sup.2+and/or Ce.sup.3+
[0092]
(Y,Lu,Gd).sub.2-tCa.sub.tSi.sub.4N.sub.6+tC.sub.1-t:Ce.sup.3+
(wherein 0.ltoreq.t.ltoreq.0.5) [0093]
3.5MgO*0.5MgF.sub.2*GeO.sub.2:Mn.sup.4+ [0094]
A.sub.2[MF.sub.6]:Mn.sup.4+, where A=Li, Na, K, Rb or Cs and M=Ge,
Si, Sn, Ti or Zr [0095]
Ca.sub.1-d-eCe.sub.dEu.sub.eAl.sub.1-d(Mg,Zn).sub.dSiN.sub.3. Those
skilled in the art can readily select other phosphor compounds
suitable for performing specific light conversions.
[0096] It should be noted that various phosphors are described
herein in which different elements enclosed in parentheses and
separated by commas, such as in the above Ca.sub.1-d
eCedEu.sub.eAl.sub.1-d(Mg,Zn).sub.dSiN.sub.3 phosphor. As
understood by those skilled in the art, this type of notation means
that the phosphor can include any or all of those specified
elements in the formulation in any ratio from 0 to 100%. That is,
this type of notation, for the above phosphor for example, has the
same meaning as
Ca.sub.1-d-eCe.sub.dEu.sub.eAl.sub.1-d(Mg.sub.1-qZn.sub.q).sub.dSiN.sub.3-
, wherein 0.ltoreq.q.ltoreq.1.
[0097] In some embodiments, a phosphor composition including
phosphor compounds Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+ and
(Ca,Sr,Ba)MgAl.sub.10O.sub.17:Eu.sup.2+,Mn.sup.2+ are employed to
produce a green light suitable for use in application such as
traffic signals. Similarly, other listed phosphors are also
suitable for producing saturated colors and/or as phosphor compound
components in white phosphor compositions.
[0098] In one embodiment, the light emitting dice or chips 12, 14,
16 are blue, violet, or ultraviolet emitters such as group
III-nitride light emitting diodes, and the phosphor 72 converts
most or substantially all of the light generated by the chips 12,
14, 16 into white light. In another embodiment the light emitting
dice or chips 12, 14, 16 are blue light emitters such as group
III-nitride light emitting diodes, and the phosphor 72 is a yellow
phosphor that converts some of the blue light into yellow light
wherein direct blue light and indirect yellow phosphor-generated
light combine to produce white light. In yet another embodiment the
light emitting dice or chips 12, 14, 16 are blue, violet, or
ultraviolet emitters and the phosphor 72 converts most or
substantially all of the emitted light into light of a selected
color, such as green, yellow, red, or so forth, so that the light
emitting package 8 produces a colored light. These are examples
only, and substantially any down-conversion of light produced by
the light emitting dice or chips 12, 14, 16 can be performed by
suitable selection of light emitting dice or chips 12, 14, 16
outputting at a selected wavelength and suitable selection of the
phosphor 72. In some embodiments, the phosphor 72 is omitted and
the direct light produced by the light emitting diodes 12, 14, 16
is the light output of the light emitting package.
[0099] In some embodiments, the light transmissive cover 60 is a
glass cover, where "glass" is not limited to silica-based materials
but rather encompasses substantially any inorganic, amorphous light
transmissive material. Making the cover 60 of glass has certain
advantages over plastic or other organic covers. Glass typically
has better thermal stability than most plastics. Glass is more
readily coated with optical coatings such as wavelength-selective
reflective coatings, wavelength-selective absorbing coatings, or
the like. Glass is also typically more resistant to scratching
compared with most plastics. Moreover, glass has particular
advantages in embodiments in which the light emitting dice or chips
12, 14, 16 produce ultraviolet or short-wavelength visible light,
because light at these wavelengths can discolor or otherwise
degrade the optical quality of light transmissive plastics over
time. Optionally, a glass is selected which provides high
reflectivity or absorption in the ultraviolet. In other
embodiments, the light transmissive cover 60 is made of plastic,
Teflon, epoxy, EVA, acrylic, or another organic light transmissive
material. In yet other contemplated embodiments, the cover 60 is
made of a crystalline light transmissive material such as
crystalline quartz. Such crystalline covers typically share many of
the advantages of glass covers.
[0100] The printed circuit board 10 can include various reflective
coatings or reflective surfaces for improving light extraction
efficiency. In some embodiments, substantially the entire surface
of the printed circuit board on which the light emitting dice or
chips 12, 14, 16 and the cover 60 are disposed is reflective for
both light produced by the light emitting chips and for light
produced by the phosphor 72. In other embodiments, that portion or
area of the printed circuit board surface covered by the cover 60
is reflective for both light produced by the light emitting chips
and for light produced by the phosphor 72, while that portion or
area of the printed circuit board surface outside of the cover 60
is reflective principally for light produced by the phosphor 72.
These latter embodiments are suitable when substantially all of the
direct light produced by the light emitting dice or chips 12, 14,
16 is converted by the phosphor, so that the output light is
substantially entirely due to the phosphor. By using different
reflective coatings or surfaces inside of and outside of the cover
60, each reflective coating or surface can be independently
optimized for the spectrum of light which it is intended to
reflect.
[0101] It will be appreciated that the term "light transmissive" as
used herein to describe the cover 60 refers to the desired light
output produced by the light emitting package 8. The light output
includes light generated by the phosphor 72, if present, responsive
to irradiation by the light emitting dice or chips 12, 14, 16. In
some embodiments, the light output includes a portion or all of the
direct light produced by the light emitting dice or chips 12, 14,
16. Examples of the latter embodiments are a white light in which
the white output light is a blending of blue light emitted by the
light emitting dice or chips 12, 14, 16 and yellow light emitted by
the phosphor 72, or embodiments in which the phosphor 72 is omitted
entirely. Where the direct light produced by the light emitting
dice or chips 12, 14, 16 contributes to the output light, the cover
60 should be at least partially light transmissive for that direct
light. In embodiments where the output light is solely produced by
the phosphor 72, on the other hand, the cover 60 may be light
transmissive for the phosphor output but partially or wholly
reflective or absorbing for the direct light produced by the light
emitting dice or chips 12, 14, 16.
[0102] An example of such a light emitting package is a white light
emitting package in which the output white light is produced by the
phosphor 72 responsive to ultraviolet light produced by the light
emitting dice or chips 12, 14, 16. The term "ultraviolet" is
intended to encompass light produced by the light emitting dice or
chips 12, 14, 16 whose peak wavelength is less than or about 425
nm. In such embodiments, including both an ultraviolet-reflective
coating on the cover 60 and an ultraviolet-reflective coating on
the printed circuit board 10 can effectively retain ultraviolet
light produced by the ultraviolet light emitting diodes within the
interior volume 70 so that the ultraviolet light has multiple
opportunities through multiple reflections to interact with the
phosphor 72, thus enhancing the ultraviolet-to-white light
conversion efficiency. For retaining light, disposing the
ultraviolet reflective coating on the inside of the cover 60 is
advantageous to avoid ultraviolet absorption losses in the cover
60. Alternatively, the ultraviolet reflecting coating can be
disposed on the outside of the cover 60, or as an embedded layer or
thin region within the cover 60.
[0103] The phosphor 72 can be applied to the inside surface of the
light transmissive cover 60 using a suitable phosphor coating
process, such as for example, electrostatic coating, slurry
coating, spray coating, or so forth. Moreover, the phosphor can be
disposed elsewhere besides on the inside surface of the cover 60.
For example, the phosphor can be applied to the outside surface of
the cover 60, using for example spray coating, outer surface
coating, or the like, or to both the inside and outside surfaces of
the cover 60. In yet another embodiment, the phosphor is embedded
in the material of the light transmissive cover 60. However,
phosphor is not readily embedded into most glass or crystalline
materials. In some embodiments the phosphor is disposed in a glass
binder that is spun onto or otherwise coated onto the inside and/or
outside surface of the cover 60.
[0104] In one suitable phosphor application process, the inside
surface of the cover 60 is prepared by treatment with a liquid or
low viscosity semi-solid material acting as a glue. The liquid
material can be, for example, liquid epoxy or silicone. The glue
material can be applied in a variety of ways, such as by spraying,
brushing, or dipping of its working formulation or a solution
thereof in a suitable solvent such as acetone, methyl isobutyl
ketone (MIBK), or t-butyl acetate. The phosphor is then deposited
by dusting, dipping or pouring of phosphor in powder form, the
choice of deposition method being based on the nature of the inside
surface of the cover 60. For example, pour phosphor powder is
suitably poured into the concave inside surface of the cover 60. On
the other hand, dipping is generally a better method for coating
the outside surface of the cover 60. The glue is then hardened by
solvent evaporation, thermal or UV curing, or the like to form the
phosphor layer.
[0105] Repetitions or various combinations of the above-described
example phosphor deposition and hardening processes may be
performed, for example to deposit more than one layer of phosphor
or multiple layers of phosphor blends, or as needed to attain a
required thickness or layered phosphor structure. Optionally, the
phosphor coating may be covered with a final layer of clear glue or
other suitable material to provide mechanical protection, to filter
out ambient ultraviolet light or excess radiation from the light
emitting dice 12, 14, 16, or so forth.
[0106] As noted previously, the light transmissive cover 60
optionally includes one or more optical coatings besides the
phosphor 72. In some embodiments, an anti-reflective coating is
applied to the inside and/or outside surface of the cover 60 to
promote light transmission. In embodiments in which the direct
light produced by the light emitting dice or chips 12, 14, 16 does
not form part of the output light, the light transmissive cover 60
optionally includes a wavelength-selective reflective coating to
reflect the direct light back into the interior volume 70 where it
has additional opportunity to interact with the phosphor 72.
[0107] In preferred embodiments, the light transmissive cover 60 is
a single piece cover, such as a single piece glass cover, a single
piece molded plastic cover, or the like. Manufacturing the cover 60
as a single piece simplifies assembly of the lighting package 8.
Another advantage of a single piece cover 60 is that a
substantially hermetic sealing of the interior volume 70 is
obtained by ensuring a substantially hermetic seal between the
perimeter 62 of the cover 60 and the printed circuit board 10. The
light transmissive cover 60 can include facets, fresnel lens
contours, or other light refractive features that promote light
scattering to produce a more spatially uniform light output.
Similarly, the light transmissive cover 60 can be made of a frosted
glass that has been etched with sand or the like to produce light
scattering. Optionally, the cover 60 includes an anti-shatter
coating such as CovRguard.TM. (available from General Electric
Company, GE Lighting Division, Nela Park, Cleveland, Ohio), Teflon,
urethane, vinyl, or so forth.
[0108] With particular reference to FIG. 3, the interior volume 70
is, in the lighting package 8, substantially filled with an
encapsulant 76. The encapsulant 76 can be, for example, a silicone
encapsulant, an epoxy encapsulant, or the like. The encapsulant 76
is at least partially light-transmissive or substantially
transparent to light produced by the light emitting dice or chips
12, 14, 16 and acts as a refractive index-matching material
promoting light extraction out of the light emitting dice or chips
12, 14, 16, and preferably also promoting light coupling with the
phosphor 72 and, if the direct light produced by the light emitting
dice 12, 14, 16 directly contributes to the package light output,
also preferably promotes light transmission into the cover 60.
[0109] In some embodiments, the phosphor is dispersed in a binding
material that is the same material as the encapsulant 76. In other
embodiments the phosphor-binding material is a different material
that has a good refractive index match with the encapsulant 76. In
yet other embodiments, the encapsulant 76 serves as the binding
material for the phosphor 72. It will be appreciated that while the
phosphor 72 is shown in FIG. 3 as residing substantially along the
inside surface of the cover 60, in some embodiments the phosphor 72
may extend some distance away from the inside surface of the cover
60 and into the encapsulant 76 disposed in the interior volume 70.
In some contemplated embodiments, the phosphor is dispersed
substantially into the encapsulant 76, and may even be uniformly
distributed throughout the encapsulant 76. However, as described in
International Publication WO 2004/021461 A2, there are efficiency
advantages to spatially separating the phosphor from the light
emitting dice or chips. Hence, in preferred embodiments the
phosphor is disposed on the inside surface of the cover 60, or is
disposed closer to the cover 60 than to the light emitting dice or
chips 12, 14, 16. In some embodiments, light-scattering particles,
particulates, or so forth are dispersed in the encapsulant 76 to
provide more uniform light distribution.
[0110] In embodiments in which the light emitting dice or chips 12,
14, 16 are bare dice, that is, are not individually encapsulated,
the encapsulant 76 provides a common encapsulation of the light
emitting dice or chips 12, 14, 16 which protects the chips from
damage due to exposure to moisture or other detrimental
environmental effects. The encapsulant 76 may also provide potting
of the light emitting dice or chips 12, 14, 16 to improve the
robustness of the lighting package 8 and make the lighting package
8 more resistant to damage from vibrations or other mechanical
disturbances.
[0111] In some embodiments the cover 60 is sealed to the printed
circuit board 10, and the encapsulant 76 is injected into the
interior volume 70 after the light transmissive cover is sealed. To
enable encapsulant injection, openings 80, 82 are provided in the
printed circuit board 10. Alternatively, openings can be provided
in the light transmissive cover or at the interface between the
perimeter of the cover and the printed circuit board. At least two
such openings 80, 82 are preferably provided, so that while
encapsulant material is injected into one opening displaced air can
exit via another opening. In other embodiments, a single elongated
or otherwise enlarged opening is used to provide room for both the
inflowing encapsulant and the outflowing displaced air.
[0112] In embodiments in which the interior volume 70 is
substantially hermetically sealed, the injected encapsulant 76 can
be a liquid or non-rigid semi-solid encapsulant, such as an optical
gel, that is contained by the hermetically sealed interior volume
70. The liquid or non-rigid semi-solid encapsulant may be left
uncured in some embodiments, since the hermetic seal prevents
leakage of the encapsulant. Moreover, a hermetic seal optionally
allows the encapsulant to be injected under some pressure, so that
the encapsulant is at a pressure higher than atmospheric pressure.
In some embodiments, the interior volume 70 is not hermetically
sealed, and some of the injected encapsulant material may leak out.
It will be appreciated that for encapsulant material of reasonably
high viscosity, the amount of leaked encapsulant material is
limited, and such leaked encapsulant material may even be
advantageous insofar as it may help seal the interior volume 70
when the injected encapsulant is cured or otherwise hardened into a
solid.
[0113] With continuing reference to FIGS. 1-3 and with further
reference to FIG. 4, an example process 100 for manufacturing the
lighting package 8 is described. The light emitting dice or chips
12, 14, 16 are mechanically and electrically connected with the
printed circuit board 10 in a die attach process 102. The die
attach can involve flip chip bonding, soldering, wire bonding, or
so forth. Separately, the inside surface (and/or optionally the
outside surface) of the light transmissive cover 60 is coated with
the phosphor 72, if such phosphor is included in the package 8, in
a phosphorizing process 104. As used herein, the term
"phosphorizing" denotes any method for putting a phosphor into the
lighting package, such as coating or spraying a phosphor
composition or compositions onto the light-transmissive cover,
suspending phosphor particles in the encapsulant, embedding a
phosphor in the light-transmissive cover, or so forth. In
embodiments in which the cover has the phosphor embedded therein,
the phosphorizing process 104 is omitted and instead the phosphor
is incorporated during molding or other formation of the cover 60.
The cover is then secured, optionally sealed, to the printed
circuit board 10 in a sealing process 106. The sealing process 106
defines the interior volume 70, which is optionally a hermetically
sealed volume. The encapsulant 76 is then injected into the
interior volume 70 through the openings 80, 82 in an encapsulant
injection process 108. The encapsulant is cured in a curing process
110 if the encapsulant material requires curing. After injection
and optional curing of the encapsulant 76, the openings 80, 82 are
optionally sealed with a suitable sealing material in a sealing
process 112. In some embodiments, the encapsulant 76 also seals the
openings 80, 82, and so in these embodiments the separate sealing
process 112 is omitted.
[0114] With reference to FIG. 5, another lighting package 8'
includes a printed circuit board 10' and a light transmissive cover
60' having an open end defining a cover perimeter 62', which are
illustrated in FIG. 5 and correspond to the printed circuit board
10, cover 60, and cover perimeter 62', respectively, of the
lighting package 8. The lighting package 8' also includes most
other components of the lighting package 8 which however are not
visible in the outside perspective view of FIG. 5. The lighting
package 8' differs from the lighting package 8 of FIGS. 1-3 in that
the electrical terminals 46 of the lighting package 8 are replaced
in the lighting package 8' by four electrical terminals 46'
disposed on the backside of the printed circuit board 10'. The
electrical terminals 46' are electrically connected with the light
emitting die or dice disposed in the cover 60' by suitable printed
circuitry residing in or on the printed circuit board 10'. The
backside electrical terminals 46' can be configured, for example,
to insert into matching openings of a four-prong surface-mount
receptacle socket.
[0115] With returning reference to FIGS. 1-3, in some embodiments
the phosphor composition 72 includes a mixture of at least two
constituent phosphor compositions each possessing essentially the
same emission color coordinates (for example x and y coordinates on
the 1931 CIE chromaticity diagram) but different color rendering
index (CRI) values. The at least two different constituent phosphor
compositions are different in that they differ by at least one
phosphor compound. For example, the first constituent phosphor
composition may include blue, green, and yellow phosphor compounds
A, B, and C, respectively, with a stoichiometry producing white or
substantially white light at a first CRI value; the second
constituent phosphor composition may include green, yellow, and red
phosphor compounds B, C, and D, respectively, with a stoichiometry
producing white or substantially white light at a second, different
CRI value. In some embodiments, the blue, green, yellow, and red
phosphor compounds A, B, C, and D are respectively
(Ba,Sr,Ca).sub.5(PO.sub.4).sub.3Cl:Eu.sup.2+,
Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+,
(Ca,Sr,Ba).sub.2Si.sub.1-cO.sub.4-2c:Eu.sup.2+ where
0.ltoreq.c<0.25, and 3.5MgO*0.5MgF.sub.2*GeO.sub.2:Mn.sup.4+.
The output converted light consisting of a blending of the
constituent converted light of the first and second phosphor
compositions has a CRI value that is different from, and possibly
larger than, the first or second CRI value of the individual
constituent phosphor compositions.
[0116] With reference to FIG. 6, which plots the 1931 CIE diagram
with the blackbody locus BB superimposed thereon, the first
phosphor composition (A,B,C) can have stoichiometries whose color
coordinates span a triangle having as vertices the color points of
the phosphor compounds A, B, and C. The second phosphor composition
(B,C,D) can have stoichiometries whose color coordinates span a
triangle having as vertices the color points of the phosphor
compounds B, C, and D. A cross-hatched triangle having as vertices
the color points of the common phosphor compounds B and C and a
third vertex E denote the range of color coordinates that can be
achieved using suitable stoichiometries of either phosphor
composition (A,B,C) or phosphor composition (B,C,D). In this range,
CRI tuning and/or luminosity tuning is achievable by blending or
combining the first and second phosphor compositions with
stoichiometries corresponding to about the same color point. This
approach enables CRI tuning by selecting the ratio of the first
(A,B,C) constituent phosphor composition and second (B,C,D)
constituent phosphor composition. More generally, at any given
color point target, at least two constituent phosphor compositions
are prepared, each constituent phosphor composition producing
constituent converted light at substantially the same color point
responsive to irradiation by emission of the light emitting die or
chip 612 (preferably but not necessarily in the ultraviolet range,
such as peak chip emission wavelength less than or about 425 nm).
The number of phosphor compounds per constituent phosphor
composition can be anywhere from one (such as, for example,
suitable phosphor compounds disclosed in U.S. Pat. No. 6,522,065)
to two, three or more (such as, for example, suitable phosphor
blends disclosed in U.S. Pat. No. 6,685,852). The disclosures of
U.S. Pat. Nos. 6,522,065 and 6,685,852 are incorporated by
reference herein in their entirety. To minimize color point
variation, the at least two different constituent phosphor
compositions should preferably provide substantially the same color
point when excited by emission of the light emitting die or chip
612, preferably to within about 0.020 units in both x and y color
coordinates on the 1931 CIE chromaticity diagram, more preferably
to within 0.010 units, and still more preferably to within 0.005
units. In some embodiments, the amount of the two constituent
phosphor compositions relative to each other is selected to
optimize the light output respective to color rendering index (CRI)
at a given minimal luminosity threshold, or vice versa, at a
selected color point.
[0117] By varying the ratio or blending of two or more constituent
phosphor compositions of substantially the same color point but
different CRI values, one can alter the final CRI and luminosity
characteristics of the device in a continuous fashion. By using a
mixture of the constituent phosphor compositions, a continuous
range of CRI values are achievable. For some such mixtures, the CRI
value of the blended light may be larger than the CRI value of any
of the constituent phosphor compositions acting alone.
Advantageously, the CRI (e.g. maximize it for a given minimal
luminosity requirement) or the luminosity (e.g. maximize it for a
given minimal CRI requirement) of the lighting device 608 is
tunable without affecting the chemical makeup of either the
phosphor compounds or the constituent phosphor compositions
configured for the color point target. This affords a set of at
least two constituent phosphor compositions to be used for the
manufacturing of white light sources with the same or similar color
point but with CRI or luminosity values customized for specific
applications. Some suitable approaches for optimizing or selecting
the CRI using two or more constituent phosphor compositions having
about the same color coordinates are disclosed in co-pending
application Ser. No. 10/909,564 filed Nov. 2, 2004 which is
incorporated by reference herein in its entirety. In some
embodiments, the at least two different constituent phosphor
compositions are selected to provide white light with color
coordinates lying on or near the blackbody locus and a color
temperature less than 4500K.
[0118] With reference to FIG. 7, in some embodiments, the at least
two different constituent phosphor compositions are selected to
blend to produce white light with a color rendering index (R.sub.a)
of 90 or greater. Example FIG. 7 shows a CRI-tuned converted light
spectrum using a mixture of the aforementioned (A,B,C) and (B,C,D)
phosphor compositions that provided a correlated color temperature
of about 3300K and a CRI value of about 90. When the blue or bluish
bleed-through direct light emitting die radiation blending with the
converted light spectrum of FIG. 7 is also accounted for, the color
temperature was about 3500K and the CRI value was about 91. Higher
or lower CRI values are attainable at the same color point or
another color point attainable by both phosphor compositions by
varying the ratio of the phosphor compositions, by using a
technique such as Design of Experiment (DOE).
[0119] It is to be appreciated that the CRI-tuning mixture of
phosphor compositions (A,B,C) and (B,C,D) is an example. Other
mixtures can be used so long as the constituent phosphor
compositions produce converted light at about the same color point
of interest. In some CRI tuned embodiments, the constituent
phosphor compositions each produce constituent converted light
which is white light or substantially white light, that is, which
lies on or substantially on the black body locus of the 1931 CIE
chromaticity diagram. Such constituent phosphor compositions are
suitably operated in conjunction with one or more ultraviolet light
emitting chips or dice, that is, with chips or dice that emit peak
radiation below or about at 425 nm. In these embodiments, the
bleed-through light produced by the at least one light emitting die
has a negligible contribution to the visible spectrum of the
converted light of the different phosphor compositions blended with
bleed-through light produced by the at least one light emitting
die. This negligible contribution can result from an arrangement in
which the conversion efficiency of the light produced by the at
least one light emitting die is close to 100%. This negligible
contribution can also result from the at least one light emitting
die emitting light substantially outside of the visible
spectrum.
[0120] In other CRI tuned embodiments, the output converted light
produced by blending of the constituent converted light of the
constituent phosphor compositions combined with radiation produced
by the at least one light emitting die that bleeds through the
phosphor layer 72 to contribute to light output of the light
emitting package 8 is white light or substantially white light,
that is, lies on or substantially on the black body locus of the
1931 CIE chromaticity diagram. In some such embodiments, the
phosphor compositions have color points corresponding to yellowish
or orangish light and are suitably operated in conjunction with one
or more blue light emitting chips or dice, that is, with chips or
dice that emit peak radiation in the blue or bluish visible range.
The bleed-through blue or bluish light combines with the yellowish
or orangish converted light to provide white light output of the
light emitting package. In other such embodiments, the phosphor
compositions produce white or substantially white light with low
intensity in the blue or bluish range, and the one or more light
emitting chips or dice emit peak radiation in the blue or bluish
visible range that bolsters the spectrum of the blended light in
the blue or bluish range of the visible spectrum.
[0121] With reference to FIG. 8, another lighting package 8''
includes a printed circuit board 10'', having a long strip shape,
on which a plurality of light emitting dice or chips 12'' are
arranged in reflective wells 22'' in a double-row arrangement along
the board strip. The printed circuit board 10'' includes one or
more printed circuitry layers 30'' sandwiched between insulative
layers 32'', 34'', and a ground plate or metal core 38''.
Electrical terminals 46'' disposed on the printed circuit board
10'' deliver electrical power to the light emitting dice or chips
12'' via the printed circuitry 30''. A light transmissive cover
60'' is tube-shaped to cover the long double-row of light emitting
dice or chips 12'' and has an open end defining a perimeter 62''
that is received by a matching groove 66'' formed in the printed
circuit board 10''. The tube-shaped cover 60'' together secured to
the printed circuit board 10'' define an elongated or tubular
interior volume 70'' containing the light emitting dice or chips
12''. A phosphor 72'' optionally coats an inside surface of the
tube-shaped cover 60''. An encapsulant 76'' substantially fills the
interior volume 70'' to encapsulate and pot the light emitting dice
or chips 12'' and the optional phosphor 72''. In some embodiments,
it is contemplated to replace the illustrated electric terminals
46'' with conventional fluorescent tube end-terminals, and to
include power-conditioning circuitry on the printed circuit board
10'' so that the lighting package 8'' is suitable for retrofit into
a fluorescent lighting fixture.
[0122] With reference to FIG. 9, yet another lighting package 208
includes a printed circuit board 210 on which one or more
(specifically three in the illustrated embodiment) light emitting
dice or chips 212 are arranged. In the lighting package 208, the
light emitting dice or chips 212 are not disposed in reflective
wells; rather, they are surface-mounted to a level surface of the
printed circuit board 210. The printed circuit board 210 includes
one or more printed circuitry layers 230 sandwiched between
insulative layers 232, 234, and a ground plate or metal core 238. A
zener diode component 244 provides electrostatic discharge
protection for the light emitting dice or chips 212. Electrical
terminals 246 disposed on the printed circuit board 210 deliver
electrical power to the light emitting dice or chips 212 via the
printed circuitry 230. A light transmissive cover 260 covers the
light emitting dice or chips 212 and has an open end defining a
perimeter 262 that is connected with the printed circuit board 210
to define an interior volume 270 containing the light emitting dice
or chips 212. A phosphor 272 optionally coats an inside surface of
the light transmissive cover 260. The above-described elements of
the lighting component or package 208 are similar to corresponding
elements of the lighting component or package 8 shown in FIGS.
1-3.
[0123] The lighting package 208 differs from the lighting package 8
in the configuration of the encapsulant disposed in the interior
volume. In the lighting package 208, a first encapsulant 276
encapsulates and optionally pots the light emitting dice or chips
212, but does not substantially fill the interior volume 270. In
some embodiments, the first encapsulant 276 may encapsulate only
the one or more light emitting dice 212. A second encapsulant 278
encapsulates the phosphor 272 if such a phosphor is included in the
package 208. In some embodiments, the second encapsulant 278 is the
binding material of the phosphor 270. For example, the phosphor 272
may be applied to the inside surface of the cover 260, and the
encapsulant in this embodiment is the binding material of the
applied phosphor. Generally, the first and second encapsulants 276,
278 can be different materials. A substantial gap 280 extends
between the first and second encapsulants 276, 278. Typically, the
gap 280 contains air; however, it is also contemplated to fill the
gap 280 with an inert gas to reduce moisture in the lighting
package 208. In yet another embodiment, the gap 280 is filled with
a third encapsulant different from at least one of the first and
second encapsulants 276, 278. In the lighting package 208, there is
no groove in the printed circuit board 210 for receiving the
perimeter 262 of the cover 260. However, such a groove similar to
the groove 66 of the lighting package 8 can optionally be provided
to align and optionally help secure the cover 260 to the printed
circuit board 210.
[0124] With continuing reference to FIG. 9 and with further
reference to FIG. 10, an example process 300 for manufacturing the
lighting package 208 is described. The light emitting dice or chips
212 are mechanically and electrically connected with the printed
circuit board 210 in a die attach process 302. The die attach can
involve flip chip bonding, soldering, wire bonding, or so forth.
The attached light emitting dice 212 are encapsulated or potted on
the printed circuit board 210 in a first encapsulation process 304,
and the first encapsulant 276 is cured in a first curing process
306 applied to the printed circuit board 210.
[0125] Separately, the inside surface (and/or optionally the
outside surface) of the light transmissive cover 260 is coated with
the phosphor 272 in a phosphorizing process 310. In embodiments in
which the cover has the phosphor embedded therein, the
phosphorizing process 310 is omitted and instead the phosphor is
incorporated during molding or other formation of the cover 260.
The phosphor is encapsulated on the light transmissive cover 260 in
a second encapsulation process 312, and the second encapsulant 278
is cured in a second curing process 314 applied to the light
transmissive cover 314. If the phosphor 272 is omitted from the
package 208, then process 310, 312, and 314 are suitably omitted.
In some embodiments the second encapsulant 278 is the binding
material of the phosphor 272; in these embodiments, the
phosphorization process 310 and the second encapsulation process
312 are integrated. The light transmissive cover is then secured,
optionally sealed, to the printed circuit board 210 in a securing
process 316. The securing process 316 defines the interior volume
270, which is optionally a hermetically sealed volume.
[0126] With reference to FIG. 11, still yet another lighting
package 408 includes a printed circuit board 410 on which a single
light emitting die or chip 412 is surface-mounted to a level
surface of the printed circuit board 410. The printed circuit board
410 includes two printed circuit traces 430, 431 disposed on the
same surface as the light emitting die 412. The two conductive
traces 430, 431 can be formed by metal evaporation or the like.
Wire bonds 436, 437 connect top-side electrodes of the light
emitting die or chip 412 with the conductive traces 430, 431. The
printed circuit board includes an insulative layer 432 on which the
two printed circuit traces 430, 431 are formed, and an optional
ground plate or metal core 438. A light transmissive cover 460
covers the light emitting die or chip 412 and has an open end
defining a perimeter 462 that is connected with the printed circuit
board 410 to define an interior volume 470 containing the light
emitting die or chip 412. The two printed circuit traces 430, 431
extend from inside the cover 460 to outside the cover 460 to
provide electrical communication into the interior volume 470. A
phosphor 472 optionally coats an inside surface of the light
transmissive cover 460, and an encapsulant 476 substantially fills
the interior volume 470. Hemispherical openings 480, 482 formed at
the perimeter 462 of the light transmissive cover 460 allow for
injection of the encapsulant material and corresponding
displacement of air. That is, the openings 480, 482 of the lighting
package 408 serve the same purpose as the printed circuit board
openings 80, 82 of the lighting package 8 (see FIG. 3).
[0127] With continuing reference to FIG. 11, a reflective coating
488 coats the inside surface of the light transmissive cover. The
reflective coating 488 is substantially reflective for light
produced by the light emitting die or chip 412 but is substantially
transmissive for light produced by the phosphor 472 responsive to
illumination by the light emitting die or chip 412. In the lighting
package 408, the phosphor 472 is disposed on the reflective coating
488 and extends some distance into the encapsulant 476.
[0128] With reference to FIG. 12, another example embodiment
lighting package 508 is shown. A common printed circuit board 510
supports a plurality of light transmissive dome-shaped covers 560
each covering one or more light emitting dice 512. Printed
circuitry of the common printed circuit board 510 connects the
light emitting dice 512 with edge terminals 446, 447 that are
adapted for connection with a DIN-type rail lighting fixture. In
other contemplated embodiments, other types of terminals are
employed. For example, the electric terminals 46 shown in FIG. 1
can be used.
[0129] In some contemplated embodiments, the printed circuit board
510 is a flexible printed circuit board, so that the light source
of FIG. 12 is a flexible sheet lighting source. In such flexible
embodiments the light emitting covers 560 provide mechanical
protection for the light emitting dice 512. In some embodiments,
the perimeter of each light transmissive dome-shaped cover 560 is
secured to the flexible printed circuit board in a manner so as to
impart tensile strain to the portion of the flexible circuit board
covered by the dome-shaped cover 560. In this way, the portions of
the flexible printed circuit board on which the light emitting dice
512 are disposed are kept substantially rigid by the tensile strain
as the flexible printed circuit board is flexed, thus reducing a
likelihood that the flexing will break the connections or bonds of
the light emitting dice 512 with the printed circuit board. In some
embodiments, the light transmissive dome-shaped covers 560 are
arranged close together such that, together with light-dispersive
properties of the covers 560, optional dispersive particles
disposed in an encapsulant within the covers 560, light spreading
provided by the distribution of phosphor across the covers 560, or
so forth, a spatially uniform planar lighting source 508 is formed
that produces little or no perceptible pixilation of the
illumination at typical illumination source-to-target
distances.
[0130] One advantage of the lighting packaging techniques disclosed
herein is flexibility in deployment of phosphor compositions. One
or more phosphor layers are readily disposed on the inner surface
of the cover, for example as described previously with respect to
phosphorization operations 104, 310 of FIGS. 4 and 10,
respectively. Application of a layer of phosphor to a glass or
plastic cover surface can be done in a precise and readily
controllable manner. Each phosphor layer suitably includes a
phosphor composition comprising one or more phosphor compounds.
[0131] With reference to FIGS. 13 and 14, a lighting package 608
includes a printed circuit board 610 supporting a light emitting
die or chip 612, or optionally more than one light emitting die or
chip, covered by a light transmissive cover 660. Thus, the lighting
package 608 is similar to the lighting package 8 of FIGS. 1-3.
However, the lighting package 608 includes two phosphor layers
L.sub.A, L.sub.B of different phosphor compositions disposed on an
inner surface of the light-transmissive dome-shaped cover 660. The
phosphor composition of phosphor layer L.sub.B is different from
the phosphor composition of layer L.sub.A in that they include at
least one different phosphor compound. The lighting package 608
optionally includes other features set forth herein with respect to
other embodiments, such as an optional ultraviolet reflective
coating 688 diagrammatically shown in FIG. 14 disposed between the
cover 660 and the phosphor layers L.sub.A, L.sub.B. The ultraviolet
reflective coating 688 is useful for embodiments in which the light
emitting die or chip 612 emits ultraviolet light while the phosphor
layers L.sub.A, L.sub.B generate visible light.
[0132] While two phosphor layers L.sub.A, L.sub.B are illustrated,
it will be appreciated that three or more phosphor layers can be
provided so as to produce light output which is a blend three or
more phosphors. The dome-shaped cover 660 provides a convenient
platform for arranging one, two, or more phosphor layers each of
which emits a spatially uniform distribution of light subtending
about 2.pi. steradians or more.
[0133] It is contemplated to employ the layered approach of FIGS.
13 and 14 in conjunction with the tunable CRI concept discussed
previously. For example, the first phosphor layer L.sub.A may
include a first constituent phosphor composition of blue, green,
and yellow phosphor compounds A, B, and C, respectively, with a
stoichiometry producing white or substantially white light at a
first CRI value, while the second phosphor layer L.sub.B may
include a second constituent phosphor composition of green, yellow,
and red phosphor compounds B, C, and D, respectively, with a
stoichiometry producing white or substantially white light at a
second, different CRI value. The layered combination of the first
constituent phosphor composition of layer L.sub.A and the second
constituent phosphor composition of layer L.sub.B produces a CRI
value that is different from, and possibly larger than, the first
or second CRI value.
[0134] CRI tuning using a single layer containing two or more
constituent phosphor compositions of about the same color point has
been described with example reference to FIG. 3. CRI tuning using a
layered structure in which each layer contains one of the
constituent phosphor compositions of about the same color point has
been described with example reference to FIGS. 13 and 14. The two
or more constituent phosphor compositions whose light is blended to
produce a tailored CRI and/or luminosity can be combined in other
physical arrangements, such as being disposed as distinct patterns
in a single layer.
[0135] With continuing reference to FIGS. 13 and 14, in some cases
one of the phosphor compositions may become saturated at high
levels of irradiation intensity by the light emitting die or chip
612. The layered arrangement of FIGS. 13 and 14 can also be useful
in addressing such saturation issues. The more easily saturated
phosphor composition is suitably arranged as the phosphor layer
L.sub.A that is furthest from the light emitting die or chip 612,
since partial absorption of light by the intervening phosphor
composition of phosphor layer L.sub.B can be expected to reduce the
excitation light flux of the phosphor composition in layer L.sub.A,
thus facilitating more efficient light conversion.
[0136] It is to be appreciated that the phosphors can be disposed
in other spatially separated arrangements besides layers. For
example, in some embodiments, the first phosphor composition may be
arranged physically as a layer disposed on an inside or outside
surface of the light-transmissive cover, while the second phosphor
composition may be dispersed in an encapsulant filling the interior
volume.
[0137] With reference to FIG. 15, a light-transmissive cover having
other than a dome-shaped geometry can be employed. FIG. 15 shows a
lighting package 708 that includes a printed circuit board 710
supporting a light emitting die or chip 712, or optionally more
than one light emitting die or chip, covered by a light
transmissive cover 760. Thus, the lighting package 708 is similar
to the lighting package 608 of FIGS. 13 and 14, except that the
light-transmissive cover 760 has a different geometry than the
dome-shaped cover 660 of FIGS. 13 and 14. The light-transmissive
cover 760 includes a reflective side portion or portions 760.sub.R
that channel light (indicated diagrammatically in FIG. 15 by two
drawn rays) toward a light-transmissive top portion 760.sub.T. Two
phosphor layers L.sub.X, L.sub.Y of different phosphor compositions
(that is, having at least one different phosphor compound) are
disposed on the light-transmissive top portion 760.sub.T.
Optionally, the two phosphor layers L.sub.X, L.sub.Y may also
extend along the inside of the reflective side portion 760.sub.R of
the light-transmissive cover 760. In some contemplated embodiments,
the phosphor layers are disposed only on the inside reflective side
portion 760.sub.R of the light-transmissive cover 760, while the
light-transmissive top portion 760.sub.T is left uncoated by
phosphor. In those of such embodiments that employ an
ultraviolet-emitting die or chip 712, the light-transmissive top
portion 760.sub.T is preferably absorbing or reflective for
ultraviolet light to prevent direct ultraviolet light from being
emitted from the lighting package 708.
[0138] With reference to FIG. 16, depending upon how the phosphor
layer or layers are disposed on the light-transmissive cover, a
logo, picture, symbol, pattern, or other depiction can be
generated. FIG. 16 shows a perspective view of another lighting
component or package similar to that of FIGS. 1-3, but having two
different phosphor compositions disposed on different regions 800,
802 screen-printed on the light-transmissive dome-shaped cover 60.
The screen-printed phosphor region 800 spells out "Acme Corp."
along with a corresponding logo, while the screen-printed phosphor
region 802 covers the area of the light-transmissive dome-shaped
cover 60 not covered by the phosphor regions 800. If, for example,
the phosphor composition of the region 800 emits red light while
the phosphor composition of the region 802 emits white light, then
when the one or more light emitting dice or chips within the cover
60 are energized, the name "Acme Corp." and corresponding logo
appears in as a red light-emissive text and symbol on a white light
emissive background. Advantageously, when using two different
phosphor compounds in respective regions to define the logo,
picture, symbol, pattern, or other depiction, both the foreground
(e.g., text or logo artwork) and the background are
light-emissive.
[0139] Some additional embodiments are disclosed as follows.
[0140] Although the discussion below with respect to embodiments of
the present invention is directed to LEDs for convenience, it
should be understood that the invention relates to the use of any
light emitting semiconductor. With reference to FIG. 17, a
conventional LED assembly is shown generally at 1010.
[0141] The LED assembly includes an LED chip 1012 mounted on a
bottom surface 1014 of the LED assembly. The LED chip 1012 emits
radiation (typically UV or blue light in a white light LED). A lens
1018 made from a transparent material surrounds the chip 1012 and
bottom surface 1014. Two lead wires 1020 connect the chip 1012 to a
source of power. Filling the space 1022 between the lens and the
chip 1012 is typically an epoxy or other transparent material (not
shown). Intimately dispersed within the epoxy are phosphor
particles (not shown) that absorb at least a portion of the light
emitted by the chip 1012 and converting it to a different
wavelength.
[0142] With reference to FIG. 18, a cross-sectional view of an
embodiment is shown. In this embodiment, an LED package is provided
generally at 1110 and includes an LED chip 1112 mounted on a
submount 1114, which in turn is mounted on a reflector 1116. As
used herein, "reflector" is meant to include not only any surface
on the bottom of the LED package, but also any other structures
meant to support the LED chip, e.g. a heat sink, etc. A lens 1118
made from a transparent material surrounds the chip 1112 and
submount 1114 and reflector 1116. Optionally filling space 1122
between the lens and the chip 1112 is typically an epoxy or other
transparent material. A phosphor layer 1124 comprising phosphor
particles is applied on an inside or outside surface of the lens
1118. The coating is preferably coated on an inside surface of the
lens to prevent the phosphor coating from being displaced by
handling, etc. The thickness of the phosphor coating should be
sufficient to convert at least a portion of the radiation emitted
by the LED chip to a different wavelength. This thickness may
typically be between 6-200 .mu.m, with a preferred thickness being
between 20-30 micron .mu.m.
[0143] The LED chip 1112 can be any conventional UV or blue light
LED. Such LEDs are known and typically consist of InGaN or AlGaN
layers epitaxially grown on a sapphire, alumina or single crystal
SiC substrate. A preferred LED chip may have a primary emission in
the range of 200-480 nm. Likewise, the phosphor layer 1124 may
include one or more suitable fluorescent phosphors capable of
absorbing the UV or blue radiation and in turn of producing, either
alone or in combination with the radiation emitted by the LED chip,
a visible white or near-white light for illumination. Suitable
phosphors for use in the present invention include, but are not
limited to, Y.sub.3AI.sub.5O.sub.2:Ce (YAG:Ce),
Tb.sub.3AI.sub.4.9O.sub.12:Ce (TAG:Ce), and
Sr.sub.4AI.sub.14O.sub.25:Eu (SAE). Other white light producing
phosphors are also suitable. The size of the phosphor particles is
not critical, and may be, by way of example, about 3-30 .mu.m in
diameter.
[0144] The lens 1118 may be made from any material that is
substantially transparent to the radiation emitted by the phosphor
and the LED chip. Thus, depending on the wavelength of the emitted
radiation, the lens may comprise various materials including, but
not limited to, glass, epoxy, plastic, thermoset or thermoplastic
resins, or any other type of LED encapsulating material known in
the art.
[0145] The providing of the phosphor coating 1124 on an inside
surface of the lens 1118 rather than dispersed in the epoxy or
other fill material provides a more uniform and efficient
conversion of the LED emission. One advantage is that a uniform
coating of controlled thickness may be applied. One benefit of this
is that coating thickness can be accurately controlled for optimum
conversion efficiency and UV bleed through (if a UV emitting chip
is used) control using a minimum amount of phosphor. This helps to
achieve uniform light emission without incidence of color rings
resulting from non-uniform dispersion of the phosphor in prior art
devices. Another benefit is that the phosphor is remote from the
heat generated by the LED, further increasing the conversion
efficiency. Of course, the phosphor layer may be positioned inside
the lens material or have a coating of another material positioned
over it, and such an arrangement is contemplated herein.
[0146] Although not intended to be limiting, the phosphor coating
may be applied by, for example, spray coating, roller coating,
meniscus or dip coating, stamping, screening, dispensing, rolling,
brushing or spraying or any other method that can provide a coating
of even thickness. A preferred method for applying the phosphor is
by spray coating.
[0147] In an exemplary technique for coating the lens and reflector
parts of the LED housing, the phosphor powder is first stirred into
a slurry, along with a binder and a solvent. Suitable binders
include, but are not limited to, silicone, epoxies, thermoplastics,
acrylics, polyimides, and mixtures thereof. Suitable solvents
include, but are not limited to, low boiling point solvents such as
toluene, methyl ethyl ketone (MEK), methylene chloride, and
acetone. The amount of each component in the slurry is not
critical, but should be chosen so as to produce a slurry that is
easily applied to the lens while also containing a sufficient
concentration of phosphor particles for efficient conversion of the
LED radiation. An exemplary slurry can be made using about 2 parts
by weight of a 6 .mu.m phosphor, 1.2 parts silicone, and 1 part
MEK. A suitable silicone is GE XE5844.
[0148] The slurry is subsequently applied to the surface of the
lens. The coated lens may then be baked, heated or otherwise
treated to remove the solvent and cure the binder. As used herein,
the term "cure" is meant to encompass not only actual curing or
crosslinking of the binder, but also more generally to indicate any
chemical and/or physical change in the binder to a state in which
the phosphor particles become relatively stationary in the binder,
typically due to a solidifying or hardening of the binder.
[0149] As noted above, the slurry can be applied to the lens via
any suitable method. In a preferred method, the slurry is applied
by spray coating. In this method, the slurry is used to fill the
reservoir of a suitable air brush. The slurry is then sprayed using
a pressurized spray gun onto the lens, which is preheated and kept
on a hot plate at an elevated temperature preferably above the
boiling temperature of the solvent, for example at about
110.degree. C. The part is sprayed by making successive passes,
which may be done at about 1/2 second per pass. The slurry dries on
contact and a uniform coating is achieved. A coating approximately
4 layers thick (about 20-30 .mu.m using 6 .mu.m size phosphor
particles) is achieved on the lens with 35-40 passes. The lens is
then baked to cure the binder. It is planned that this approach to
coating LED's would be used for any LED's for general illumination.
If desired, a second coating of a transparent material may be added
over the phosphor layer to protect the phosphor or to provide an
overcoating to help light extraction.
[0150] A significant improvement in light output has been achieved
using blue LED's with the YAG phosphor over the conventional
coating method wherein the phosphor is embedded in the slurry and
uniformly applied around the chip. Clearly there are many other
ways to remotely the lens surrounding an LED chip. These would be
considered within the scope of this invention.
[0151] In one preferred embodiment, the lens preferably has a
radius that is at least about 2-3 times the length ("L") of one
side of the chip. This arrangement increases the likelihood that
radiation generated or reflected off a coating applied to such a
lens is more likely to strike other parts of the coating, where it
will be retransmitted, rather than the chip or other non-coated
area, where it will be absorbed and lost.
[0152] In a second embodiment, illustrated in FIG. 19, an LED
package is again provided at 1210 and includes an LED chip 1212
mounted on a submount 1214, which in turn is mounted on a reflector
1216. A lens 1218 surrounds the chip 1212 and submount 1214 and
reflector 1216. Optionally filling space 1222 between the lens and
the chip 1212 is typically an epoxy or other transparent material.
To further improve efficiency, a phosphor coating 1224 comprising
phosphor particles is applied on an inside surface of the lens 1218
and on the top surface of the reflector 1216. The top surface of
the reflector, which may be thought of as the bottom of the
package, is preferably first coated with a reflective layer 1240,
such as a high dielectric powder, such as, alumina, titania, etc. A
preferred reflective material is Al.sub.2O.sub.3. The phosphor
layer 1224 is then placed over the reflective layer 1240 on top of
the reflector. The use of the reflective layer 1240 serves to
reflect any radiation 1242 that penetrates the phosphor layer 1224
on this surface. Alternately, instead of coating the transparent
lens 1218 with a separate phosphor layer 1224, the phosphor may
instead be intimately dispersed within the material comprising the
transparent hemisphere.
[0153] The phosphor layer 1224 over the reflective layer 1240 on
the reflector 1216 is preferably relatively thick, i.e. greater
than 5 layers of powder, while the phosphor layer on the curved top
of the hemisphere may be adjusted to achieve a desired color and to
absorb all radiation incident on it. In general the phosphor layer
on the top of the hemisphere will range between 1-4 layers thick in
the case of blue emitting chips in order that some of the blue
radiation be emitted. In the case of UV chips the layer of phosphor
coating on the hemisphere should be 4-8 layers thick in order to
absorb at least most of the UV radiation emitted by the chip.
[0154] As shown in FIG. 19, radiation from the chip 1242 is
prevented from leaving the structure without first striking the
phosphor coated surface of the hemisphere. Further, the total
phosphor coated surface area is much greater than the surface area
of the emitting chip, preferably at least 10 times the exposed
surface area of the absorbing parts of the LED chip. As used
herein, the exposed surface area of the absorbing parts of the LED
include the exposed surface are of the LED chip as well as any
exposed surface of the submount not covered with a reflective layer
and/or a phosphor layer.
[0155] In such an arrangement, although there may be a significant
amount of blue or UV radiation scattered back into the hemisphere,
nearly all this radiation, which is diffusely scattered, strikes
other parts of the phosphor coating rather than the chip or
submount. Most of the visible light generated by the phosphor
coating also is directed back into the hemisphere. Also there is no
metallic reflector and no exposed lead structure. The important
feature of this geometry is that everything except the LED chip
1212 is phosphor covered and the phosphor surface area of the
hemisphere is much larger, preferably greater than 10 times, the
surface area of any absorbing parts of the LED. Therefore, nearly
all radiation going back into the hemisphere will strike other
phosphor-coated areas and be either reflected or absorbed and
retransmitted by the phosphor. The embodiments disclosed herein are
calculated to have an efficiency greater than 70%, and in most
cases approaching 100%.
[0156] In Table 1 the efficiency of this design is compared with
several standard LED package geometries. These comparisons were
made using a computer simulation. The computer simulation is a flux
model described below. It considers all the radiation fluxes and
assumes that all are diffuse so that the amount of radiation
incident on any given surface is proportional to its area. As shown
in Table 1 the geometry described above provides a package
efficiency of essentially 100%.
TABLE-US-00001 TABLE 1 Comparison of Calculated Package
Efficiencies of Two Standard Configurations of Phosphor Coated
LED's with 3 Embodiments Disclosed in the Present Invention Package
Milliwatts/ Efficiency lumen SiC Al.sub.2O.sub.3 SiC
Al.sub.2O.sub.3 LED Description substrate substrate substrate
substrate 1.6 mm.sup.2 chip + 27 mm.sup.2 58% 70% 6.7 5.6 reflector
+ phosphor on chip 1.6 mm.sup.2 chip + 69% 80% 5.7 4.9 phosphor on
chip 1.6 mm.sup.2 chip + 27 mm.sup.2 82% 88% 4.7 4.4 reflector +
phosphor on lens (FIG. 5) 1.6 mm.sup.2 chip + 3 mm 98% 99% 4 3.9
radius hemisphere (FIG. 3) 1.6 mm.sup.2 chip + 3 mm 99% 100% 3.9
3.9 radius sphere (FIG. 4)
[0157] FIG. 20 shows an embodiment operating under the same
principle. Here an LED chip 1312 is mounted on a pedestal 1314
which also serves as the heat sink. However, the chip 1312 is
placed at the center of a molded sphere 1318. A phosphor layer (not
shown) is then coated on the inside surface 1320 of the sphere 1318
or, alternately, intimately dispersed within the sphere. In this
design the LED will radiate uniformly in all directions. Again, it
is clear that both blue/UV radiation and visible radiation
generated by the phosphor coating and scattered back into the
sphere will be more likely to strike other phosphor coated surfaces
in preference to striking either the chip 1312 or the pedestal
1314. These light absorbing structures are small targets for the
diffuse radiation. As seen in Table 1, the package efficiency is
close to 100% for this arrangement. The lower package efficiency
for LED structure on SiC substrates are due to greater absorption
of the LED radiation by the SiC substrate as compared to the
Al.sub.2O.sub.3 substrate.
[0158] From the previous embodiments. It is apparent that the
specific shape of the phosphor coating is not important as long as
it surrounds as completely as possible the LED chip and is a
distance sufficient from this chip (e.g. a distance such that the
phosphor coated surface has a surface area greater than about 10
times the exposed surface area of the chip) such that radiation
scattered from the coating is unlikely to strike the chip or chip
structures. The invention is not limited to the embodiments
described herein but intended to embrace all such coating shapes,
and preferably wherein the phosphor covered surfaces has
approximately 10 times the exposed area of the absorbing parts of
the LED or greater. Thus, the lens on which the phosphor is coated
is not limited to hemispherical or spherical, but can include any
geometric shape, preferably with the phosphor coated surface area
being about at least 10 times the exposed area of the absorbing
parts of the LED.
[0159] The invention is also intended to cover geometries which are
not so ideal and perhaps do not give the full advantage of 100%
package efficiency but nevertheless do utilize the principle of a
remote phosphor coating designed so that the coated surface is at
least 10 times the emitting area of the chip. For example FIG. 21
shows a schematic of a conventional surface mount LED. In this
arrangement, the LED chip 1412 and submount 1414 are mounted in a
reflector cup 1416. Unlike the conventional design, which has the
phosphor embedded more or less randomly in an optical medium
between reflector and the lens, the phosphor coating is applied as
a layer on a transparent lens 1418. The phosphor coating is remote
from the chip 1412 and on a surface with about >10 times the
exposed area of the absorbing parts of the LED. Obviously, the
surface of the lens 1418 on which the phosphor coating is applied
can have a surface area less than 10 times the surface area of the
chip. However, the package efficiency of the assembly will be
reduced accordingly, since more of the radiation will strike and be
absorbed by the chip. A second lens 1430 can be mounted over the
phosphor coated lens for protection.
[0160] Most of the UV or blue radiation and visible radiation which
is scattered back from the phosphor coating strikes either the
reflector cup 1416 or other phosphor surface. Only a relatively
small amount strikes the light absorbing chip and submount. In this
design it is important that the reflector cup 1416 be made of a
very highly reflective material, for example a vapor deposited and
protected silver coating with greater than 95% reflectivity or an
inorganic powder of high purity, such as finely divided alumina or
titania. In addition the reflector cup 1416 may or may not be
coated with the phosphor. Table 1 shows the simulated performance
of a specific LED with an area of 1.6 mm.sup.2 on a submount in a
silver reflector cup utilizing a phosphor coated lens of area of 27
mm.sup.2.
[0161] As shown in FIGS. 22 and 23, the present invention also
discloses the concept of a remote phosphor coating as applied to
systems containing multiple LED chips. Multiple blue or UV emitting
LED's can be mounted on a single reflective electrical interconnect
board or other structure. A phosphor coated surface then is used to
surround not a single LED but the entire set of LED's. The phosphor
coated surface may be used alone or in combination with other
highly reflecting surfaces to surround the set of LED's. Two
examples of such structures are shown in FIGS. 22 and 23. One is a
power module 1500 which might be used as a downlight. The other is
a panel lamp 1600 with many LED's 1602 mounted behind a phosphor
coated panel 1604. It is clear that many such arrangements could be
made provided that the phosphor surface area is the preferred 10
times the exposed area of the absorbing parts of the LED.
[0162] As detailed above, any of the embodiments may include an
epoxy or other transparent filler between the LED chip and the
phosphor coated lens. More efficient extraction of light can be
realized when the refractive index of the encapsulant or
transparent filler is closely matching the geometric mean of the
refractive indexes of the die and the lens, preferably within about
20% of this value, and even more preferably within about 10%. This
reduces the amount of internal reflections in the lamp. Thus, in
the case of a GaN LED chip having a refractive index of about 2.7
with a lens having a refractive index of about 1.5, the filler will
preferably have a refractive index of from about 2.1. In the case
of an LED chip having two or more materials having different
refractive indices, such as a GaN semiconductor on a sapphire
submount having a refractive index of about 1.7, the refractive
index of the encapsulant will preferably match the geometric mean
of the lens and the higher of the two. Better light extraction can
thus be achieved with encapsulants having a higher index of
refraction than epoxy, such as spin-on glass (SOG) or other high
refractive index materials.
[0163] Any of the above embodiments can also be equipped with one
or more band pass filters to further improve the efficiency of the
resulting LED package. Thus, in one embodiment, as shown in FIG.
25, a lens 1718 for a blue LED source is shown containing a first
band pass filter 1750. The band pass filter is positioned between
the phosphor layer 1724 and the LED (not shown). The band pass
filter is selected such that the incident light 1752 from the blue
LED source is allowed to pass while the light 1754 emitted from the
phosphor layer 1724 is reflected outward.
[0164] In the embodiment shown in FIG. 26, two band pass filters
are provided in a UV LED source package. In this embodiment, a
first band pass filter 1850 is positioned between the phosphor
layer 1824 and the LED source (not shown) adjacent a lens 1818. The
first band pass filter acts to transmit the UV light 1852 from the
LED while reflecting the light 1854 emitted from the phosphor layer
1824. A second band pass filter 1856 reflects the UV light 1852
from the LED while allowing the light 1854 emitted from the
phosphor layer 1824 to pass. This arrangement prevents the
transmission of potentially harmful UV radiation from the package
while ensuring transmission of visible light.
[0165] As seen in FIG. 27, an array of micro or macro lenses 1960
may be formed on the outer surface of the lens 1918 in any of the
above embodiments to control the emission angle, direction or
intensity of the emitted radiation 1952 and 1954.
[0166] The calculation results shown in Table 1 are based on a
linear flux model illustrated in the FIG. 24. The figure shows nine
fluxes incident on four surfaces of the LED package. These fluxes
are described by the nine linear equations below, with each
equation describing the flux with the corresponding number. The
equations are:
L.sub.3.sup.out=L.sub.3.sup.+t.sub.3.sup.VIS Flux F1:
L.sub.3.sup.-=L.sub.3.sup.+r.sub.3.sup.VIS+I.sub.3.sup.+a.sub.3.sup.UVQ(-
.lamda..sub.I/.lamda..sub.L)1/2) Flux F2:
L.sub.3.sup.+=L.sub.2.sup.-p.sub.2
3+L.sub.1.sup.-p.sub.13+L.sub.0.sup.-p.sub.0
3+I.sub.3.sup.+a.sub.3.sup.UVQ(.lamda..sub.1/.lamda..sub.L)1/2 Flux
F3:
L.sub.2.sup.+=L.sub.3.sup.-p.sub.3
2+L.sub.1.sup.-p.sub.12+L.sub.0.sup.-p.sub.0
2+I.sub.2.sup.+a.sub.2.sup.UVQ(.lamda..sub.1/.lamda..sub.L)1/2 Flux
F4:
L.sub.2.sup.-=L.sub.2.sup.+r.sub.2.sup.VIS Flux F5:
L.sub.1.sup.+=L.sub.3.sup.-p.sub.31
+L.sub.2.sup.-p.sub.21+L.sub.0.sup.-p.sub.0 1 Flux F6:
L.sub.1.sup.-=L.sub.1.sup.+r.sub.1.sup.VIS Flux F7:
L.sub.0.sup.+=L.sub.3.sup.-p.sub.3 0+L.sub.2.sup.-p.sub.2
0+L.sub.1.sup.-p.sub.1 0 Flux F8:
L.sub.0.sup.-=L.sub.0.sup.+r.sub.0.sup.VIS Flux F9:
These surfaces are:
[0167] 3=the upper phosphor coated surface,
[0168] 2=the lower phosphor coated surface,
[0169] 1=the reflector and submount, and
[0170] 0=the blue or UV emitting chip.
[0171] There are nine other equations describing the blue or UV
fluxes. The equations describing the blue or UV fluxes are not
shown. They are coupled to the visible light equations through the
quantum efficiency Q and the Stoke's s shift (.lamda.i/.lamda.I).
The eighteen linear equations result in eighteen unknowns, i.e. the
relative powers of radiation striking each surface, and are solved
simultaneously.
[0172] The p values are the probabilities that radiation from one
surface will strike another. In the calculations shown in Table 1
these were taken to be the ratios of surface areas. Q is the
quantum efficiency of the phosphor. .lamda. is the average
wavelength of the blue or UV chip radiation or the average
wavelength of the visible emission of the phosphor.
[0173] The other parameters needed are the reflectivities and
absorptivities of the different material surfaces. These were
obtained either from Handbook values or were measured directly
using known methods. There are no values for the reflectivities of
the chips and so these were calculated by assuming that each chip
consisted of the semiconductor layers and substrate. All radiation
incident on the chip was assumed to be normal and incident on the
substrate in a flip-chip design and diffraction effects were
ignored. Up to second order the expression for the reflectivity of
the chip is then:
R=R.sub.sub+(1-R.sub.sub).sup.2 exp(-2 a.sub.sub
t.sub.sub)R.sub.act+(1-R.sub.sub).sup.2 exp(-2 a.sub.sub t.sub.sub)
(1-R.sub.act).sup.2 exp(-2 a.sub.act t.sub.act) R.sub.mst
where: [0174] R.sub.sub=reflectivity of substrate
R.sub.act=reflectivity of active layers [0175] a.sub.sub=absorption
cost of sub a.sub.act=absorption coefficient of active layers
[0176] t.sub.sub=thickness of substrate t.sub.act=thickness of
active layers Known or estimated values were used for the indices
of refraction, the absorption coefficients and thicknesses.
Thus,
[0176] R=((n1-n2).sup.2+k.sup.2)/(n1+n2).sup.2+k.sup.2), where
k=.lamda.a/2.pi..
[0177] The invention has been described with reference to the
preferred embodiments. Obviously, modifications and alterations
will occur to others upon reading and understanding the preceding
detailed description. It is intended that the invention be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or the
equivalents thereof.
The appended claims follow:
* * * * *