U.S. patent application number 13/106304 was filed with the patent office on 2011-09-01 for light emitting diode packages, light emitting diode systems and methods of manufacturing the same.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to YuSik Kim.
Application Number | 20110210367 13/106304 |
Document ID | / |
Family ID | 41266148 |
Filed Date | 2011-09-01 |
United States Patent
Application |
20110210367 |
Kind Code |
A1 |
Kim; YuSik |
September 1, 2011 |
LIGHT EMITTING DIODE PACKAGES, LIGHT EMITTING DIODE SYSTEMS AND
METHODS OF MANUFACTURING THE SAME
Abstract
In a method of forming an LED semiconductor device, and in an
LED semiconductor device, an LED is provided on a substrate. A
first encapsulant material layer is provided on the LED, and the
first encapsulant material layer is firstly annealed. A
luminescence conversion material layer is provided on the firstly
annealed first encapsulant material layer, and the first
encapsulant material layer and the luminescence conversion material
layer and secondly annealed.
Inventors: |
Kim; YuSik; (Suwon-si,
KR) |
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
41266148 |
Appl. No.: |
13/106304 |
Filed: |
May 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12380134 |
Feb 24, 2009 |
7955879 |
|
|
13106304 |
|
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Current U.S.
Class: |
257/98 ;
257/E33.067 |
Current CPC
Class: |
H01L 33/0095 20130101;
H01L 33/507 20130101; H01L 33/52 20130101; H01L 2224/48091
20130101; H01L 2224/73265 20130101; H01L 2924/00014 20130101; H01L
2224/48091 20130101 |
Class at
Publication: |
257/98 ;
257/E33.067 |
International
Class: |
H01L 33/50 20100101
H01L033/50 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2008 |
KR |
10-2008-0042424 |
Claims
1. An LED semiconductor device comprising: an LED on a substrate; a
first encapsulant material layer on the LED; and a luminescence
conversion material layer consisting essentially of a luminescence
conversion material on the first encapsulant material layer, the
luminescence conversion material layer being of a thickness that is
selected to determine a resultant transmittance of optical energy
that is emitted from the LED.
2. The device of claim 1: wherein the first encapsulant material
layer is first annealed under first process conditions to have a
first hardness prior to application of the luminescence conversion
material layer and wherein the thickness of the luminescence
conversion material layer is determined as a result of the first
hardness; and wherein the first encapsulant material layer and the
luminescence conversion material layer are second annealed under
second process conditions, that are independent of the first
process conditions.
3. The device of claim 2 wherein the first process conditions of
the first annealing result in a soft curing of the first
encapsulant material layer and wherein the second process
conditions of the second annealing result in a hard curing of the
first encapsulant material layer.
4. The device of claim 2 wherein the thickness of the luminescence
conversion material layer is determined by controlling process
conditions of the first annealing of the first encapsulant material
layer.
5. The device of claim 1 wherein the thickness of the luminescence
conversion material layer is determined by applying a physical
pressure to the first encapsulant material layer.
6. The device of claim 1 further comprising a second encapsulant
material layer on the luminescence conversion material layer.
7. The device of claim 6 wherein the second encapsulant material
layer is substantially transparent to optical energy at wavelengths
emitted by the LED.
8. The device of claim 1 wherein the first encapsulant material
layer is substantially transparent to optical energy at wavelengths
emitted by the LED.
9. The device of claim 1 further comprising a filter on the
luminescence conversion material layer.
10. The device of claim 1 further comprising one or more lenses on
the luminescence conversion material layer.
11. The device of claim 1 wherein the first encapsulant material
layer is further on the substrate.
12. The device of claim 1 wherein the first encapsulant material
layer is exclusively present on the LED and not on the
substrate.
13. The device of claim 12 further comprising a second
encapsulation layer on the luminescence conversion material layer
and on the substrate.
14. The device of claim 13 wherein the second encapsulation layer
is shaped to have a convex or concave shape.
15. The device of claim 13 further comprising a filter on the
second encapsulation layer.
16. The device of claim 1 wherein the luminescence conversion
material comprises a phosphor material.
17. The device of claim 1 wherein the transmittance is within a
range between about 5% and 10%.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 12/380,134, filed on Feb. 24, 2009, which
claims the benefit of Korean patent application number
10-2008-0042424, filed on May 7, 2008, in the Korean Intellectual
Property Office, the contents of which applications are
incorporated herein in their entirety by reference
BACKGROUND
[0002] Light emitting diodes (LEDs) enjoy widespread use in modern
electronic devices. They are capable of emitting high-power light
and offer more efficient power consumption, higher reliability,
greater durability, and longer life, as compared to their
conventional counterparts, including fluorescent lamps,
incandescent bulbs, and halogen lamps. In addition, owing to their
relatively small size, they can be configured in relatively small
form factors.
[0003] In a conventional LED, a forward bias is applied to a p-n
junction, causing holes in the p-type semiconductor material to
recombine with electrons in the n-type semiconductor material. As a
result of the recombination, optical energy is emitted at a
wavelength that corresponds to the bandgap of the p-n junction.
[0004] For many LED applications, it is commonly desired to
generate white light. There are a number of approaches for
accomplishing this. In one approach, LEDs that generate red, green,
and blue light, or LEDs that generate blue and yellow light, are
combined in a single package to generate white light. This approach
can lead to bulky packaging and complicated manufacturing
procedures, since it requires the formation, electrical connection,
and packaging of multiple LEDs in a fixed area.
[0005] In another approach, the output of a blue LED is made to be
incident on a yellow phosphorescent material to generate a white
output light as a result of the phosphorescent reaction.
Alternatively, the output of an ultraviolet LED is made to be
incident on a phosphorescent material including red, green and blue
phosphorescent particles to generate a white output light as a
result of the phosphorescent reaction. In these approaches, it can
be difficult to control the quality of the white output light,
since it depends highly on the concentration of the phosphorescent
material. For example, in conventional approaches, the
phosphorescent material is commonly mixed into a resin material
that encases the LED in the package. This approach suffers from low
color repeatability and therefore low reliability, since it is
difficult to control the concentration of the phosphorescent
material once it is mixed with the resin carrier.
SUMMARY OF THE INVENTION
[0006] Embodiments of the present invention are directed to light
emitting units, packages and systems employing such light emitting
units, and methods of manufacturing the same, that address and
overcome the limitations associated with conventional devices and
methods. Specifically, the devices, systems and methods in
accordance with the present invention provide for high color
repeatability in the resulting LED devices, while reducing the
amount of luminescence conversion material needed, thereby reducing
fabrication costs. In particular, the transmittance and conversion
efficiency of the resulting LED devices can be optimized by
controlling a thickness of a luminescence conversion material layer
present in the devices where wavelength conversion of optical
energy occurs.
[0007] In one aspect, a method of forming an LED semiconductor
device comprises: providing an LED on a substrate; providing a
first encapsulant material layer on the LED; first annealing the
first encapsulant material layer; providing a luminescence
conversion material layer on the firstly annealed first encapsulant
material layer; and second annealing the first encapsulant material
layer and the luminescence conversion material layer.
[0008] In one embodiment, the luminescence conversion material
layer consists essentially of a luminescence conversion
material.
[0009] In another embodiment, providing the luminescence conversion
material layer on the firstly annealed first encapsulant material
layer comprises providing the luminescence conversion material
layer to a thickness that is selected to determine a resultant
transmittance of optical energy that is emitted from the LED
semiconductor device.
[0010] In another embodiment, the method further comprises
controlling a thickness of the luminescence conversion material
layer by controlling process conditions of the first annealing of
the first encapsulant material layer.
[0011] In another embodiment, the method further comprises
controlling a thickness of the luminescence conversion material
layer by applying a physical pressure to the first encapsulant
material layer.
[0012] In another embodiment, the first annealing is performed
under first process conditions, and the second annealing is
performed under second process conditions, and the second process
conditions are independent of the first process conditions.
[0013] In another embodiment, the first process conditions of the
first annealing result in a soft curing of the first encapsulant
material layer and the second process conditions of the second
annealing result in a hard curing of the first encapsulant material
layer.
[0014] In another embodiment, the method further comprises
providing a second encapsulant material layer on the luminescence
conversion material layer.
[0015] In another embodiment, the second encapsulant material layer
is substantially transparent to optical energy at wavelengths
emitted by the LED.
[0016] In another embodiment, providing a second encapsulant
material layer on the luminescence conversion material layer occurs
prior to second annealing the first encapsulant material layer and
the luminescence conversion material layer.
[0017] In another embodiment, providing a second encapsulant layer
on the luminescence conversion material layer occurs after second
annealing the second encapsulant material layer and the
luminescence conversion material layer.
[0018] In another embodiment, the first encapsulant material layer
is substantially transparent to optical energy at wavelengths
emitted by the LED.
[0019] In another embodiment, the method further comprises
selectively removing a portion of the luminescence conversion
material layer after providing the luminescence conversion material
layer on the firstly annealed first encapsulant material layer,
wherein selectively removing removes a portion of the luminescence
conversion material layer that is not adhered to the firstly
annealed first encapsulant material layer.
[0020] In another embodiment, the method further comprises
providing a filter on the luminescence conversion material
layer.
[0021] In another embodiment, the method further comprises
providing one or more lenses on the luminescence conversion
material layer.
[0022] In another embodiment, providing a first encapsulant
material layer on the LED further comprises providing a first
encapsulant material layer on the substrate.
[0023] In another embodiment, providing a first encapsulant
material layer on the LED further comprises providing the first
encapsulant material layer exclusively on the LED and the substrate
and patterning the first encapsulant material so that the first
encapsulant material remains exclusively on the LED.
[0024] In another embodiment, providing the luminescence conversion
material layer on the firstly annealed first encapsulant material
layer further comprises providing the luminescence conversion
material layer on the substrate; and the method further comprises:
selectively removing a portion of the luminescence conversion
material layer after providing the luminescence conversion material
layer on the firstly annealed first encapsulant material layer and
the substrate, wherein selectively removing removes a portion of
the luminescence conversion material layer that is not adhered to
the firstly annealed first encapsulant material layer.
[0025] In another embodiment, the method further comprises
providing a second encapsulant layer on the luminescence conversion
material layer and on the substrate.
[0026] In another embodiment, the method further comprises shaping
the second encapsulation layer to have a convex or concave
shape.
[0027] In another embodiment, the method further comprises
providing a filter on the second encapsulation layer.
[0028] In another embodiment, luminescence conversion material of
the luminescence conversion material layer comprises a phosphor
material.
[0029] In another aspect, an LED semiconductor device comprises: an
LED on a substrate; a first encapsulant material layer on the LED;
and a luminescence conversion material layer consisting essentially
of a luminescence conversion material on the first encapsulant
material layer, the luminescence conversion material layer being of
a thickness that is selected to determine a resultant transmittance
of optical energy that is emitted from the LED.
[0030] In one embodiment, the first encapsulant material layer is
first annealed under first process conditions to have a first
hardness prior to application of the luminescence conversion
material layer and wherein the thickness of the luminescence
conversion material layer is determined as a result of the first
hardness; and the first encapsulant material layer and the
luminescence conversion material layer are second annealed under
second process conditions, that are independent of the first
process conditions.
[0031] In another embodiment, the first process conditions of the
first annealing result in a soft curing of the first encapsulant
material layer and the second process conditions of the second
annealing result in a hard curing of the first encapsulant material
layer.
[0032] In another embodiment, the thickness of the luminescence
conversion material layer is determined by controlling process
conditions of the first annealing of the first encapsulant material
layer.
[0033] In another embodiment, the thickness of the luminescence
conversion material layer is determined by applying a physical
pressure to the first encapsulant material layer.
[0034] In another embodiment, the device further comprises a second
encapsulant material layer on the luminescence conversion material
layer.
[0035] In another embodiment, the second encapsulant material layer
is substantially transparent to optical energy at wavelengths
emitted by the LED.
[0036] In another embodiment, the first encapsulant material layer
is substantially transparent to optical energy at wavelengths
emitted by the LED.
[0037] In another embodiment, the device further comprises a filter
on the luminescence conversion material layer.
[0038] In another embodiment, the device further comprises one or
more lenses on the luminescence conversion material layer.
[0039] In another embodiment, the first encapsulant material layer
is further on the substrate.
[0040] In another embodiment, the first encapsulant material layer
is exclusively present on the LED and not on the substrate.
[0041] In another embodiment, the device further comprises a second
encapsulation layer on the luminescence conversion material layer
and on the substrate.
[0042] In another embodiment, the second encapsulation layer is
shaped to have a convex or concave shape.
[0043] In another embodiment, the device further comprises a filter
on the second encapsulation layer.
[0044] In another embodiment, the luminescence conversion material
comprises a phosphor material.
[0045] In another aspect, a system comprises: a controller that
generates LED activation signals; and a plurality of LED
semiconductor devices, the LED semiconductor devices receiving LED
activation signals from the controller, each LED semiconductor
device comprising: an LED on a substrate; a first encapsulant
material layer on the LED; and a luminescence conversion material
layer consisting essentially of a luminescence conversion material
on the first encapsulant material layer, the luminescence
conversion material layer being of a thickness that is selected to
determine a resultant transmittance of optical energy that is
emitted from the LED, when the LED is activated by the LED
activation signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The foregoing and other objects, features and advantages of
the embodiments of the invention will be apparent from the more
particular description of preferred embodiments of the invention,
as illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention. In the
drawings:
[0047] FIGS. 1A-1E are cross-sectional diagrams illustrating the
formation of an LED structure, in accordance with an embodiment of
the present invention.
[0048] FIG. 2 is a flow diagram illustrating the steps for forming
an LED, in accordance with an embodiment of the present
invention.
[0049] FIG. 3 is a conceptual illustration of a physical force
provided to apply the luminescence conversion material to the
soft-cured encapsulant, in accordance with an embodiment of the
present invention.
[0050] FIG. 4 is a cross-sectional diagram of another embodiment of
the present invention.
[0051] FIGS. 5A and 5B are cross-sectional diagrams of other
embodiments of the present invention.
[0052] FIGS. 6A-6E are cross-sectional diagrams illustrating the
formation of an LED structure, in accordance with another
embodiment of the present invention.
[0053] FIGS. 7A-7C are cross-sectional diagrams of other
embodiments of the present invention.
[0054] FIG. 8A is a perspective view of a LED structure package in
accordance with an embodiment of the present invention. FIGS. 8B-8D
are cross-sectional views of the LED structure package of FIG. 8A,
taken along section line I-I' of FIG. 8A, in accordance with
various embodiments of the present invention.
[0055] FIGS. 9A and 9B are cross-sectional views of an LED package
module, in accordance with various embodiments of the present
invention.
[0056] FIG. 10A is a top view and FIGS. 10B and 10C are perspective
views, respectively, of LED array package modules, in accordance
with various embodiments of the present invention.
[0057] FIG. 11 is an exploded cross-sectional view of an LED
system, in a display panel application, accordance with an
embodiment of the present invention.
[0058] FIGS. 12A-12D are views of LED systems, in accordance with
other embodiments of the present invention.
[0059] FIG. 13 is a block diagram of an LED system, in accordance
with embodiments of the present invention.
[0060] FIG. 14A is a plot of phosphor conversion efficiency as a
function of phosphor thickness for experimental results obtained
from sample embodiments prepared in accordance with the present
invention. FIG. 14B is a plot of phosphor conversion efficiency as
a function of output at UV wavelengths following application of the
green phosphor conversion layer for experimental results obtained
from sample embodiments prepared in accordance with the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0061] Embodiments of the present invention will now be described
more fully hereinafter with reference to the accompanying drawings,
in which preferred embodiments of the invention are shown. This
invention may, however, be embodied in different forms and should
not be construed as limited to the embodiments set forth herein.
Like numbers refer to like elements throughout the
specification.
[0062] It will be understood that, although the terms first,
second, etc. are used herein to describe various elements, these
elements should not be limited by these terms. These terms are used
to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of the present invention. As used herein, the term "and/or"
includes any and all combinations of one or more of the associated
listed items.
[0063] It will be understood that when an element is referred to as
being "on" or "connected" or "coupled" to another element, it can
be directly on or connected or coupled to the other element or
intervening elements can be present. In contrast, when an element
is referred to as being "directly on" or "directly connected" or
"directly coupled" to another element, there are no intervening
elements present. Other words used to describe the relationship
between elements should be interpreted in a like fashion (e.g.,
"between" versus "directly between," "adjacent" versus "directly
adjacent," etc.). When an element is referred to herein as being
"over" another element, it can be over or under the other element,
and either directly coupled to the other element, or intervening
elements may be present, or the elements may be spaced apart by a
void or gap.
[0064] The terminology used herein is for the purpose of describing
particular embodiments and is not intended to be limiting of the
invention. As used herein, the singular forms "a," "an" and "the"
are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises," "comprising," "includes" and/or
"including," when used herein, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0065] FIGS. 1A-1E are cross-sectional diagrams illustrating the
formation of an LED, in accordance with an embodiment of the
present invention. FIG. 2 is a flow diagram illustrating the steps
for forming an LED, in accordance with an embodiment of the present
invention.
[0066] Referring to FIG. 1A and step 502 of FIG. 2, a package
substrate 10 is prepared to include a slot or opening 12. The
package substrate 10 can include an optional sub-mount 30 in a
central region of the package for locating an LED 20. The LED 20
can be mounted to the optional sub-mount 30, or, in other
embodiments, mounted directly to the package substrate 10. In
various embodiments, the LED can be configured to generate optical
energy, for example optical energy at ultraviolet or blue
wavelengths. The slot 12 can be configured with tapered sidewalls
12a as shown to increase the light emitting efficiency of the
resulting package.
[0067] Referring to FIG. 1B and step 504 of FIG. 2, a first
encapsulant 50, or resin layer, is provided in the opening 12. In
this embodiment, the first encapsulant 50 is provided at least to a
level or depth that coats or covers the LED 20. The first
encapsulant 50 can comprise a material that is transparent to the
optical energy at the wavelengths emitted by the LED 20. In various
embodiments, the first encapsulant 50 can comprise at least one of
epoxy, silicone, rigid silicone, urethane, oxethane, acryl,
polycarbonate, polyimide, and a mixture of at least two of these,
suitable for protecting the underlying LED 20.
[0068] Referring to FIG. 1B and step 506 of FIG. 2, a first
annealing 90 is performed on the resulting structure, including the
first encapsulant 50. The process conditions of the first annealing
90, including temperature, pressure, and duration, are selected so
that a soft-curing of the first encapsulant 50 is achieved. In a
soft-cured state, the first encapsulant 50 is no longer in a fluid
state and is not fully hardened. Instead, the first encapsulant 50
is made to be sufficiently hard by the first annealing 90 so that
when a luminescence conversion material, such as a phosphor
material, is later applied to a top surface of the first
encapsulant 50, the luminescence conversion material does not
penetrate substantially into the first encapsulant 50, but rather,
the luminescence conversion material bonds to a top surface, or top
region, of the first encapsulant 50. In an example where the first
encapsulant 50 comprises a silicone epoxy material in a 1
mm.times.1 mm top-view-type LED package, a first annealing process
performed at 150 C-200 C, at atmospheric pressure, and for a
duration of 80-120 seconds was found to sufficiently soft-cure the
first encapsulant 50. The process conditions of the first annealing
90 vary with the type of first encapsulant and the volume of first
encapsulant 50 in the opening 12; in general, a larger volume of
first encapsulant requires a longer annealing time.
[0069] Referring to FIG. 1C and step 508 of FIG. 2, a luminescence
conversion material 60a is applied to the resulting soft-cured
first encapsulant 50. In one embodiment, the luminescence
conversion material 60a comprises a powder-type substance that is
applied using a deposition process. The luminescence conversion
material 60a can be applied to the soft-cured first encapsulant 50
under a physical force, such as a thermal stress or mechanical
pressure so that a lower portion of the luminescence conversion
material 60a is physically pushed into, or bonded to, the upper
surface of the soft-cured first encapsulant 50. FIG. 3 is a
conceptual illustration of a physical force F provided by member 62
to apply the luminescence conversion material 60a to the soft-cured
first encapsulant 50. Since the first encapsulant 50 is in a
soft-cured state, and is not hardened, the upper surface thereof is
receptive of the luminescence conversion material 60a, and
particles of the luminescence conversion material 60a bond
thereto.
[0070] The luminescence conversion material 60a operates to absorb
first optical energy at first wavelengths emitted by the LED and
converts the absorbed optical energy to second optical energy
having second wavelengths that are different than the first
wavelengths. For example, to generate second optical energy at
white-light wavelengths, the first wavelength of the LED can be
blue and the luminescence conversion material 60a can comprise
yellow fluorescent material. To further increase the color
rendering index (CRI) of the resulting package, red phosphor can be
added to the luminescence conversion material 60a. In another case,
second optical energy at white-light wavelengths can be generated
where the first wavelength of the LED is ultraviolet by applying
red/green/blue phosphor material to the luminescence conversion
material 60a.
[0071] Referring to FIG. 1D and step 510 of FIG. 2, excess
luminescence conversion material 60a is removed from the upper
surface of the first encapsulant 50. This step can be performed,
for example, by shaking or vibrating the resulting package in an
upside-down position and allowing excess particles or material to
be removed by gravity. In another technique, a gas stream under
pressure, for example, an Ar, Ne, or N.sub.2 gas stream, can be
applied to the luminescence conversion material 60a to remove
excess material from the upper surface of the first encapsulant 50.
As a result, a luminescence conversion material layer 60 remains on
an upper surface of the first encapsulant 50. The resulting
luminescence conversion material layer 60 consists essentially of
luminescence conversion material 60a because the material 60a is
applied to the top surface of the first encapsulant 50, and is not
applied as a mixture along with the material of the first
encapsulant 50. The application of a luminescence conversion
material layer 60 consisting essentially of luminescence conversion
material 60a is distinguished from the conventional approaches for
forming LED structures in that the luminescence conversion material
layer 60 is not mixed directly with the resin, or first
encapsulant, but instead is applied as a layer to a top surface of
the soft-cured first encapsulant 50, as described above. The term
"consisting essentially of" is intended to mean including primarily
luminescence conversion material, but allowing for a certain low
percentage of impurities or other materials to be present in the
resulting luminescence conversion material layer 60.
[0072] It has been demonstrated experimentally that the thickness
of the resulting luminescence conversion material layer 60
determines the conversion efficiency of the resulting device, where
the conversion efficiency is the power ratio between the converted
optical energy (i.e., the power of the light emitted at the second
wavelength, or light converted as a result of passing through the
luminescence conversion material layer 60) and the original optical
energy (i.e., the power of the light emitted at the first
wavelength, or the wavelength generated by the LED) for the optical
energy emitted from the package. A higher conversion efficiency
indicates that relatively more light is converted by the
luminescence conversion material layer 60, and relatively less
light at the first wavelength emitted by the LED is emitted from
the package without conversion.
[0073] It has also been determined that the conversion efficiency
of a device is directly related to the thickness of the
luminescence conversion material layer 60, and an optimal
conversion efficiency can be determined for a given device
configuration. For example, if the luminescence conversion material
layer 60 is too thin, then conversion efficiency decreases since
optical energy at the first wavelength will pass through the
luminescence conversion material layer 60 without conversion. At
the same time, if the luminescence conversion material layer 60 is
too thick, then conversion efficiency decreases since the amount of
optical energy passing through the luminescence conversion material
layer 60 with wavelength conversion and the first wavelength will
decrease.
[0074] For similar reasons, it has also been determined that the
thickness of the resulting luminescence conversion material layer
60 is directly related to the transmittance of the optical energy
at the first wavelength of the resulting device, where the
transmittance of a device is the power ratio between the optical
energy of the light emitted by the LED at the first wavelength to
the optical energy of the light passing through the luminescence
conversion material layer 60 and emitted from the package at the
first wavelength (i.e., unconverted light energy). It has been
determined that since the transmittance of a device is directly
related to the thickness of the luminescence conversion material
layer 60, an optimal transmittance value can be determined for a
given device configuration. For example, a thinner luminescence
conversion material layer 60 results in a larger transmittance for
the resulting device and a thicker luminescence conversion material
layer 60 results in a smaller transmittance for the resulting
device. The thickness of the luminescence conversion material can
be determined based on a suitable transmittance range at a maximum
conversion efficiency range, for example, a transmittance in a
range of between about 5% and 10%. Other transmittance ranges are
possible and may be desirable in certain applications.
[0075] Embodiments of the present invention allow for control of,
and therefore optimization of, the thickness of the resulting
luminescence conversion material layer 60 by controlling the
hardness of the soft-cured first encapsulant 50. In general, a
first encapsulant layer 50 that is cured to a lesser extent, is
less hard, and is receptive to more luminescence conversion
material 60a, resulting in a larger thickness in the resulting
luminescence conversion material layer 60. Similarly, a first
encapsulant layer 50 that is cured to a greater extent, is more
hard, and is less receptive to luminescence conversion material
60a, resulting in reduced thickness in the resulting luminescence
conversion material layer 60. The process conditions of the first
annealing 90 are directly related to the resulting hardness of the
first encapsulant layer 50 at the time of application of the
luminescence conversion material 60a, and therefore, are directly
related to the resulting thickness of the luminescence conversion
material layer 60.
[0076] The resulting luminescence conversion material layer 60 is
relatively thin, which confers a number of advantages. First, its
thickness, being relatively thin, can be more readily controlled,
which leads to greater color repeatability in the manufacturing
process. Second, a relatively thin layer leads to improved
thickness uniformity across the top surface of the first
encapsulant layer, leading to more uniform color output by a given
device. Third, since relatively less material is used for the
layer, material costs during fabrication can be reduced.
[0077] Referring to FIG. 1E and step 512 of FIG. 2, an optional
second encapsulant layer 70, for example, a passivation layer, is
formed on the resulting luminescence conversion material layer 60.
The second encapsulant layer 70 operates to protect the underlying
luminescence conversion material layer 60 from external
environmental conditions, for example, from exposure to moisture.
In various embodiments, the second encapsulant layer 70 can be
formed to be substantially flat, or can be formed to include
various optical features, as will be described below in connection
with further embodiments. The second encapsulant layer 70 can
comprise, for example, a material that is transparent to the
converted optical energy emitted by the luminescence conversion
material layer 60 including at least one of: epoxy, silicone,
urethane, oxethane, acryl, polycarbonate, polyimide, and a mixture
of at least two of these, suitable for protecting the underlying
luminescence conversion material layer 60.
[0078] Referring to FIG. 1E and step 514 of FIG. 2, a second
annealing process 92 is performed on the resulting structure,
including the soft-cured first encapsulant 50, the luminescence
conversion material layer 60, and the second encapsulant layer 70.
The process conditions of the second annealing 92, including
temperature, pressure, and duration, are selected so that a
hard-curing of the first encapsulant 50 is achieved for the
resulting LED device 1. In a hard-cured state, the first
encapsulant 50 is substantially fully hardened. In an example where
the first encapsulant comprises a silicone epoxy material in a 7
mm.times.7 mm top-view-type LED package (chip size is 1 mm.times.1
mm), a second annealing process performed at 150 C-200 C, at
atmospheric pressure, for a duration of 5 to 30 minutes was found
to sufficiently hard-cure the first encapsulant 50. In this
example, the duration of the second annealing process as much
longer than the duration of the first annealing process. Other
process parameters such as temperature and/or pressure may be
adjusted to achieve hard-curing of the resulting device. The
process conditions of the second annealing 92 vary with the type of
first encapsulant and the volume of first encapsulant 50 present;
in general, a larger volume of first encapsulant requires a longer
annealing time for the second annealing step.
[0079] Referring to FIG. 1E and steps 516 and 518 of FIG. 2, in
another embodiment, the second annealing 92 can be optionally
performed prior to formation of the second encapsulant layer
70.
[0080] FIG. 4 is a cross-sectional diagram of another embodiment of
the present invention. Referring to FIG. 4, an optional wavelength
filter 80 can be applied in the optical path of the emitted optical
energy, for example, on the passivation layer 70, in order to
filter the optical energy emitted by the device 2. In one example,
the wavelength filter 80 can be applied to absorb optical energy
that is emitted at a certain wavelength or wavelengths. In one
example, the filter can be tuned to absorb the first optical energy
emitted by the LED 20, and to be transparent to the second optical
energy that is converted and emitted by the luminescence conversion
material layer 60. In a case where the LED generates first optical
energy at ultraviolet wavelengths, the filter 80 can be configured
to absorb energy at ultraviolet wavelengths, preventing human
exposure to harmful ultraviolet energy. In certain applications,
the filter can be configured to dissipate heat. In alternative
embodiments, an organic or inorganic dye can be applied to the
filter to intercept or pass a specific wavelength or color, for
example for use in stage or theater illumination or in traffic
light applications.
[0081] FIGS. 5A and 5B are cross-sectional diagrams of other
embodiments of the present invention. In these embodiments, the
second encapsulant layer 70 is formed in a lens shape to perform an
optical function. In the embodiment of FIG. 5A, the second
encapsulant layer 70 is formed in a single convex lens shape to
provide for dispersion of optical energy emitted by the LED
structure 3. In the embodiment of FIG. 5B, the second encapsulant
layer 70 is formed as a multiple convex lens configuration to
provide for greater dispersion of optical energy emitted by the LED
structure 4. The second encapsulant layer 70 can also be formed in
the shape of other suitable optical elements to perform a desired
optical function for the device 3, 4.
[0082] FIGS. 6A-6E are cross-sectional diagrams illustrating the
formation of an LED structure, in accordance with another
embodiment of the present invention.
[0083] Referring to FIG. 6A and step 502 of FIG. 2, a package
substrate 10 is prepared to include a slot or opening 12, as
described above. The package substrate 10 can include an optional
sub-mount 30 in a central region of the package for locating an LED
20. The LED 20 can be mounted to the optional sub-mount 30, or, in
other embodiments, mounted directly to the package substrate 10. In
various embodiments, the LED can be configured to generate optical
energy, for example optical energy at ultraviolet or blue
wavelengths. The slot 12 can be configured with tapered sidewalls
12a as shown to increase the light emitting efficiency of the
resulting package.
[0084] Continuing to refer to FIGS. 6A and 6B, and referring now to
step 504 of FIG. 2, a first encapsulant 52, or resin layer, or
encapsulant layer 52a, is provided in the opening 12 to cover the
LED 20. Referring to FIG. 6B, in this embodiment, the first
encapsulant 52 does not fill the opening to a level above an upper
surface of the LED 20. Instead, the first encapsulant 52 of the
present embodiment is provided to exclusively cover the LED 20 and
a region immediately surrounding the LED 20, for example, covering
the region of the device that lies above the submount or substrate
30, as shown. In one embodiment, the first encapsulant 52 is
selectively applied to the LED 20 and submount 30, and not to the
package substrate 10. Referring to FIG. 6A, in another embodiment,
the encapsulant layer 52a is applied to the entire opening 12,
including the package substrate 10, the LED 20 and the submount 30,
and is then selectively patterned 53 so that the first encapsulant
52 remains exclusively on the LED 20 and optionally at regions
immediately surrounding the LED 20. As in the above-described
embodiment of FIGS. 1A-1E, the first encapsulant 52 can comprise a
material that is transparent to the optical energy at the
wavelengths emitted by the LED 20. In various embodiments, the
first encapsulant 52 can comprise at least one of epoxy, silicone,
rigid silicone, urethane, oxethane, acryl, polycarbonate,
polyimide, a mixture of at least two of these, suitable for
protecting the underlying LED 20.
[0085] Continuing to refer to FIG. 6B and referring now to step 506
of FIG. 2, as in the above-described embodiment, a first annealing
90 is performed on the resulting structure, including the first
encapsulant 52. The process conditions of the first annealing 90,
including temperature, pressure, and duration, are selected so that
a soft-curing of the first encapsulant 52 is achieved. In a
soft-cured state, the first encapsulant 52 is no longer in a fluid
state and is not fully hardened. Instead, the first encapsulant 52
is made to be sufficiently hard by the first annealing 90 so that
when a luminescence conversion material, such as a phosphor
material, is later applied to a top surface of the first
encapsulant 52, the luminescence conversion material does not
penetrate substantially into the first encapsulant 52, but rather,
the luminescence conversion material bonds to a top surface or top
region of the first encapsulant 52. Process conditions of the first
annealing 90 can be determined as described above in connection
with the embodiment of FIGS. 1A-1E.
[0086] Referring to FIG. 6C and step 508 of FIG. 2, a luminescence
conversion material 60a is applied to the resulting soft-cured
first encapsulant 52. In one embodiment, the luminescence
conversion material 60a comprises a powder-type substance that is
applied using a deposition process. The luminescence conversion
material 60a can be applied to the soft-cured first encapsulant 52
under a physical force, for example in the manner shown above in
connection with FIG. 3, such as a thermal stress or mechanical
pressure so that a lower portion of the luminescence conversion
material 60a is physically pushed into, or bonded to, the upper
surface of the soft-cured first encapsulant 52. Since the first
encapsulant 52 is in a soft-cured state, and is not hardened, the
upper surface thereof is receptive of the luminescence conversion
material 60a, and particles of the luminescence conversion material
60a bond thereto.
[0087] Referring to FIG. 6D and step 510 of FIG. 2, excess
luminescence conversion material 60a is removed from the upper
surface of the first encapsulant 52, for example, in the manner
described above in connection with FIG. 1D. As a result, a
luminescence conversion material layer 60 remains on an upper
surface of the first encapsulant 52. Also, the luminescence
conversion material layer 60 consists essentially of luminescence
conversion material 60a, as described above in connection with the
embodiment of FIG. 1D. The thickness of the resulting luminescence
conversion material layer 60 determines the conversion efficiency
of the resulting device, as described above in connection with the
embodiment of FIGS. 1A-1E.
[0088] Referring to FIG. 6E and step 512 of FIG. 2, an optional
second encapsulant layer 70, for example, a passivation layer, is
formed on the resulting luminescence conversion material layer 60.
The second encapsulant layer 70 operates to protect the underlying
luminescence conversion material layer 60 from external
environmental conditions, for example, protection from exposure to
moisture. In various embodiments, the second encapsulant layer 70
can be formed to be substantially flat, or can be formed to include
various optical features, as will be described below in connection
further embodiments. The second encapsulant layer 70 can comprise,
for example, materials described above in connection with the
description of the embodiment of FIGS. 1A-1E.
[0089] Continuing to refer to FIG. 6E and referring now to step 514
of FIG. 2, a second annealing process 92 is performed on the
resulting structure, including the soft-cured first encapsulant 52,
the luminescence conversion material layer 60, and the second
encapsulant layer 70. The process conditions of the second
annealing 92, including temperature, pressure, and duration, are
selected so that a hard-curing of the first encapsulant 50 is
achieved. In a hard-cured state, the first encapsulant 52 is
substantially fully hardened for the resulting LED device 5. As in
the above described embodiment of FIGS. 1A-1E, the process
conditions of the second annealing 92 vary with the type of first
encapsulant and the volume of first encapsulant 52 present; in
general, a larger volume of first encapsulant 52 requires a longer
annealing time for the second annealing step.
[0090] Continuing to refer to FIG. 6E and referring now to steps
516 and 518 of FIG. 2, in another embodiment, the second annealing
92 can be optionally performed prior to formation of the second
encapsulant layer 70.
[0091] FIGS. 7A-7C are cross-sectional diagrams of other
embodiments of the present invention. In these embodiments, the
second encapsulant layer 70 is formed in a lens shape to perform an
optical function. In the embodiments shown, an optional wavelength
filter 80 is applied in the optical path of the emitted optical
energy, for example, on the passivation layer 70 in order to filter
the optical energy emitted by the device 6, 7, 8. In the embodiment
of FIG. 7A, the second encapsulant layer 70 is formed in a concave
single lens shape to provide for focusing of optical energy emitted
by the LED structure 6. In the embodiment of FIG. 7B, the second
encapsulant layer 70 is formed in a convex single lens shape to
provide for dispersion of optical energy emitted by the LED
structure 7. In the embodiment of FIG. 7C, the second encapsulant
layer 70 is formed as a highly convex single lens configuration to
provide for greater dispersion of optical energy emitted by the LED
structure 8. Also, in the FIG. 7C embodiment, the LED 20 and
submount 30 are mounted to a flat package substrate 10, rather than
in a slotted package substrate, which can be desirable for certain
applications.
[0092] FIG. 8A is a perspective view of a LED structure package in
accordance with an embodiment of the present invention. FIGS. 8B-8D
are cross-sectional views of the LED structure package of FIG. 8A,
taken along section line I-I' of FIG. 8A, in accordance with
various embodiments of the present invention. The various
embodiments are shown for illustrative purposes, and the
embodiments of the present invention are not limited thereto.
[0093] Referring to FIG. 8A, a first lead 14a and a second lead 14b
of the LED package are coupled to the LED 20 to apply a bias
voltage or current thereto to cause the generation of optical
energy by the LED 20. The first and second leads 14a, 14b can be
formed, for example, of a thermally conductive material so that
they operate to remove heat from the LED package.
[0094] Referring to FIG. 8B, in one embodiment, the first lead 14a
and second lead 14b are isolated from the package substrate 10 by
insulation layer 11. In this example, the submount 30 lies on the
first lead 14a, isolated therefrom by insulation layer 31. Bonding
wire 16a couples the first lead 14a to the first junction of the
LED 20, and bonding wire 16b couples the second lead 14b to the
second junction of the LED 20.
[0095] Referring to FIG. 8C, in another embodiment, the submount 30
is mounted on both the first lead 14a and the second lead 14b,
isolated therefrom by insulation layer 31. Interlayer vias 32
extending through the submount 30 respectively couple the first
lead 14a to the first junction of the LED 20 and the second lead
14b to the second junction of the LED 20.
[0096] Referring to FIG. 8D, in another embodiment, the submount 30
is mounted on both the first lead 14a and the second lead 14b,
isolated therefrom by insulation layer 31. Interlayer surface
interconnects 34 respectively couple the first lead 14a to the
first junction of the LED 20 and the second lead 14b to the second
junction of the LED 20. The embodiments of FIGS. 8C and 8D are
conducive to smaller package geometries.
[0097] FIGS. 9A and 9B are cross-sectional views of an LED package
module, in accordance with various embodiments of the present
invention. The various embodiments are shown for illustrative
purposes, and the embodiments of the present invention are not
limited thereto.
[0098] Referring to FIG. 9A, an LED package 1, for example, an LED
package configured as described above in connection with FIG. 4 and
FIG. 8B, is mounted to a circuit board 300 to provide an LED
package module 101. The first lead 14a of the LED package 1 is
electrically coupled to a first conductor 310 of the circuit board
300 and the second lead 14b of the LED package 1 is electrically
coupled to a second conductor 320 of the circuit board 300. The
first and second conductors 310, 320 are in turn coupled to a main
driving system on the circuit board, or in communication with the
circuit board 300.
[0099] Referring to FIG. 9B, another embodiment of the LED package
module 102 is similar to the LED package module described above in
connection with FIG. 9A, the exception being that the circuit board
300 in the present example includes first and second interlayer
vias 316, 326 respectively connecting the first and second first
and second conductors 310, 320 on a first side of the circuit board
300 to third and fourth conductors 312, 322 on a second side of the
circuit board 300.
[0100] FIG. 10A is a top view and FIGS. 10B and 10C are perspective
views, respectively, of LED array package modules, in accordance
with various embodiments of the present invention. The various
embodiments are shown for illustrative purposes, and the
embodiments of the present invention are not limited thereto.
[0101] Referring to FIG. 10A, an LED package array 103 includes
columns of LED packages 1 having first and second leads 14a, 14b
respectively coupled to each other by first and second conductive
interconnects 310, 320. In this manner, LED packages 1 sharing a
column are activated to emit optical energy at the same time. The
first and second conductive interconnects 310, 320 of respective
columns can likewise be coupled together so that the LED packages
of all columns can be activated to emit at the same time.
[0102] Referring to FIG. 10B, cylindrical lenses 340 formed of
encapsulation material can be formed along the columns, or
alternatively, across the columns, of LED packages formed on a
common substrate 300, to perform optical functions as desired.
Referring to FIG. 10B, in this embodiment, the LED packages along
columns or rows of the array are configured with individual convex
lenses 350 formed of encapsulation material to provide another
optical function for the array.
[0103] FIG. 11 is an exploded cross-sectional view of an LED system
in a display panel application, in accordance with an embodiment of
the present invention. Conventionally, this type of system is an
edge type back light unit (BLU) in a liquid crystal display (LCD)
device. In this embodiment, an LED package 1 or LED package array
is mounted to a circuit board 300. The LED package 1 can be a
side-view type. A transfer sheet 410 can be made of a transparent
plastic resin, such as acrylic and receives the emitted optical
energy and operates as a waveguide to present the optical energy to
a reflective sheet 412 having a pattern 412a thereon. The reflected
optical energy is emitted from a side region of the transfer sheet
and is incident on a spreading sheet 414, which operates to
disperse the optical energy. A plurality of prism sheets 416
operate to further guide the emitted optical energy toward a
display panel 450 so that the energy is primarily orthogonal to a
direction of extension of the panel 450.
[0104] FIGS. 12A-12D are views of LED systems, in accordance with
other embodiments of the present invention.
[0105] Referring to FIG. 12A, another example application of an LED
system in accordance with an embodiment of the present invention is
illustrated. In this example, a projector system 505 includes a
light source 510 in turn including an LED package 1 of the type
described herein. The emitted light is incident on a condensing
lens 520 and is applied to a color filter 530. A sharping lens 540
directs the light to an image modulating device, for example, a
digital micromirror device (DMD) which modulates the applied light
by the desired image and presents reflected light to a projection
lens 580. The projection lens 580 in turn directs the
image-modulated light to a projection screen 590.
[0106] Referring to FIG. 12B, another example application of an LED
system in accordance with an embodiment of the present invention is
illustrated. In this example, the LED system of the present
invention including LED packages 1 of the type described above is
applied to an automobile headlight, auxiliary light or tail-light
system 610.
[0107] Referring to FIG. 12C, another example application of an LED
system in accordance with an embodiment of the present invention is
illustrated. In this example, the LED system of the present
invention including LED packages 1 of the type described above is
applied to a street lamp, or traffic lamp, system 620.
[0108] Referring to FIG. 12D, another example application of an LED
system in accordance with an embodiment of the present invention is
illustrated. In this example, the LED system of the present
invention including LED packages 1 of the type described above is
applied to an illumination lighting system 630, such as a spot
light or flood light.
[0109] FIG. 13 is a block diagram of an LED system, in accordance
with embodiments of the present invention. Referring to FIG. 13, an
LED system includes an LED controller 702, for example, an LED
controller that generates LED activation signals that activate and
deactivate one or more LED devices 706. The activation signals 704
comprise, for example, the driving signals that forward bias the
LED devices 706 so that they emit optical energy. The LED devices
706, of the type described herein, can be activated individually,
for example in display applications, or can be arranged in an array
and activated collectively, for example in illumination
applications. The LED controller 702 can be addressed and
programmed by a processing system having memory, according to
well-known data processing configurations.
[0110] In the various embodiments described herein, the LED can
comprise any of a number of suitable types of LEDs, including, for
example, In.sub.xAl.sub.yGa.sub.(1-x-y) (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1) LEDs. In various embodiments, the LED can be
configured, for example, as a flip-chip type LED, a vertical type
LED or a lateral type LED, and the LED package can be configured as
a top-view type package or a side-view type package, for example.
Contemporary LED chips for top-view type LED packages are commonly
square-shaped, such as 1 mm.times.1 mm in size, and are
particularly applicable to lighting systems, window illumination,
and automobile head lamps. Contemporary LED chips for side-view
type LED packages are usually rectangle-shaped such as 250
.mu.m.times.600 .mu.m in size, and find application in mobile
display systems, such as mobile telephones, MP3 players and
navigation systems.
[0111] The LED can be configured to generate any of a number of
narrow-band or broad-band wavelengths of optical energy, including,
for example, ultraviolet or blue wavelengths. Uniform chromaticity
can be achieved, for example, by mounting the LED in a central
region of the package substrate 10.
[0112] In the various embodiments described herein, the package
substrate 10 can comprise any of a number of suitable materials,
including, for example, an organic material having lightfast
characteristics, for example, silicone resin, epoxy, acryl resin,
urea-formaldehyde resin, imide resin, or fluororesin.
Alternatively, the package substrate 10 can comprise an inorganic
material having lightfast characteristics, for example, glass or
silica gel. The package substrate 10 can be treated by a
thermosetting process so that the resulting structure resists heat
generated during device fabrication. Filler materials, such as AlN
or AlO can be added to the material of the package substrate 10 to
alleviate thermal stress that can be generated during later
application and annealing of the first and second encapsulant
layers. In other embodiments, metal or ceramic material can be
applied to at least a portion of the package substrate 10 to
increase heat dissipation properties of the resulting package.
[0113] In the various embodiments described herein, the
luminescence conversion material 60a of the luminescence conversion
material layer 60 can comprise any of the following or mixtures any
of the following: [0114] Nitride/oxide material activated by
lanthanide, such as Eu, Ce etc., [0115] M.sub.2Si.sub.5N.sub.8:Eu,
M.sub.2Si.sub.5N.sub.8:Eu, MSi.sub.7N.sub.10:Eu,
M.sub.1.8Si.sub.5O.sub.0.2N.sub.8:Eu,
M.sub.0.9Si.sub.7O.sub.0.1N.sub.10:Eu, MSi.sub.2O.sub.2N.sub.2:Eu
[0116] (where M is selected from Sr, Ca, Ba, Mg, Zn) [0117]
Alkaline earth halogen apatite activated by lanthanide, transition
metal (Mn etc.,). [0118] M.sub.5(PO.sub.4).sub.3X:R [0119] (where M
is Sr, Ca, Ba, Mg, Zn; X is F, Cl, Br, I; R is Eu, Mn, Eu) [0120]
Alkaline earth metal-boride halogen phosphor. [0121]
M.sub.2B.sub.5O.sub.9X:R [0122] (where M is Sr, Ca, Ba, Mg, Zn; X
is F, Cl, Br, I; R is Eu, Mn, Eu) [0123] Alkaline earth
metal-aluminate phosphor. [0124] SrAl.sub.2O.sub.4:R,
Sr.sub.4Al.sub.14O.sub.25:R, CaAl.sub.2O.sub.4:R,
BaMg.sub.2Al.sub.16O.sub.27:R, BaMg.sub.2Al.sub.16O.sub.12:R,
BaMgAl.sub.10O.sub.17:R [0125] (where R is Eu, Mn, Eu) [0126]
Alkaline earth silicate phosphor. [0127] (SrBa).sub.2SiO.sub.4:Eu
[0128] Alkaline earth emulsificate phosphor. [0129]
La.sub.2O.sub.2S:Eu, Y.sub.2O.sub.2S:Eu, Gd.sub.2O.sub.2S:Eu [0130]
Alkaline earth thiogallate phosphor. [0131] Alkaline earth nitrided
silicon phosphor. [0132] Germanate [0133] Rare earth aluminate,
rare earths silicate activated by lanthanide, such as Ce, Eu.
[0134] Y.sub.3Al.sub.5O.sub.12:Ce,
(Y.sub.0.8Gd.sub.0.2).sub.3Al.sub.5O.sub.12:Ce,
Y.sub.3(Al.sub.0.8Ga.sub.0.2).sub.5O.sub.12:Ce, (Y, Gd).sub.3(Al,
Ga).sub.5O.sub.12 [YAG] [0135] Tb.sub.3Al.sub.5O.sub.12:Ce,
Lu.sub.3Al.sub.5O.sub.12:Ce [0136] ZnS:Eu, Zn.sub.2GeO.sub.4:Mn,
MGa.sub.2S.sub.4:Eu [0137] (where M is Sr, Ca, Ba, Mg, Zn; X is F,
[0138] Activating material can be changed or added: [0139]
Eu.fwdarw.Tb, Cu, Ag, Au, Cr, Nd, Dy, Co, Ni, Ti
[0140] The luminescence conversion material 60a can also comprise
another material well-suited for wavelength conversion of optical
energy.
[0141] An experiment was conducted to determine whether the
conversion efficiency value for an LED device can be optimized by
controlling the thickness of the luminescence conversion material
layer. The experiment included a 7 mm.times.7 mm top view LED
package (1 mm.times.1 mm chip size), including a ultraviolet
emitting LED and green phosphor material for the luminescence
conversion material. The LED 20 was encased in a first encapsulant
layer 50 comprising a transparent silicone resin, which filled the
package opening 12 by about 90 percent. A first annealing operation
90 was performed to soft-cure the first encapsulant layer 50 at a
temperature of 165 C for 100 seconds. A green phosphor material was
provided as the luminescence conversion material 60a, excess
luminescence conversion material 60a was removed to provide a
luminescence conversion material layer 60, and the resultant was
subjected to a second annealing operation 92 at a temperature of
165 C for 5 minutes in order to hard-cure the resulting device 1.
Five such samples were prepared, each having resulting green
phosphor thicknesses that were experimentally measured and
different. The resulting green phosphor thickness was managed by
applying a controlled mechanical pressure to the luminescence
conversion material 60a, as described above. As a result, Samples 1
through 5 having green phosphor thicknesses of 226 .mu.m, 224
.mu.m, 190 .mu.m, 153 .mu.m and 108 .mu.m respectively, as shown in
Table 1 below, were provided.
[0142] Referring to the data of Table 1 below, a laboratory
measurement of the output power of the optical energy of the LED at
ultraviolet (UV) wavelengths was performed for each sample (Samples
1-5) before application of the green phosphor layer. In Table 1, it
can be seen that the output energies at UV wavelengths of Samples
1-5 were 149 mW, 145 mW, 148 mW, 148 mW, and 147 mW, respectively,
as shown in Table 1 below.
[0143] Next, a laboratory measurement of the output power of the
optical energy at the ultraviolet (UV) wavelengths was performed
for each sample (Samples 1-5) following application of the green
phosphor layer. In Table 1, it can be seen that the output energy
at UV wavelengths of the five samples were measured to be 4.3 mW,
4.6 mW, 7.5 mW, 11.1 mW, and 14.6 mW respectively, as shown in
Table 1 below.
[0144] Also, a laboratory measurement of the output power of the
optical energy at the converted green wavelengths was performed for
each sample (Samples 1-5) following application of the green
phosphor layer. In Table 1 it can be seen that the converted output
energy at green wavelengths of the five samples were measured to be
67 mW, 74 mW, 91.3 mW, 106.8 mW, and 88 respectively, as shown in
Table 1 below.
[0145] For each sample, the conversion efficiency of the resulting
LED device, or, in this case, since phosphor was used as the
luminescence conversion material layer, the phosphor conversion
efficiency (PCE), can be calculated as:
PCE=output at green wavelengths/output at UV wavelengths(pre
phosphor-post phosphor)
For example, for Sample 1:
PCE=67 mW/(149 mW-4.3 mW)=46.3%
PCE values for each sample (Samples 1-5) were calculated as 46.3%,
52.7%, 65%, 78%, and 66.5% respectively.
[0146] At the same time, the transmittance of each sample (Samples
1-5) was calculated as:
Transmittance = output at UV wavelengths ( post phosphor ) output
at UV wavelengths ( pre phosphor ) ##EQU00001##
For example, for Sample 1,
Transmittance=4.3 mW/149 mW=2.9%
Transmittance values for each sample (Samples 1-5) were calculated
as 2.9%, 3.2%, 5%, 7.5%, and 10% respectively.
[0147] FIG. 14A is a plot of phosphor conversion efficiency (PCE)
as a function of phosphor thickness for experimental results
obtained from sample embodiments prepared in accordance with the
present invention; and FIG. 14B is a plot of phosphor conversion
efficiency (PCE) as a function of output at UV wavelengths
following application of the green phosphor conversion layer for
experimental results obtained from sample embodiments prepared in
accordance with the present invention.
[0148] Referring to FIGS. 14A and 14B, it can be seen that an
optimum PCE for the experimental device occurs under the process
conditions of Sample 4 S4. It can also be seen that when the PCE
has a value ranging from 80% of the maximum value of about 78 to
about 120% of the maximum value, the phosphor thickness of the
sample (ranging from 200 .mu.m to 100 .mu.m for Samples 3-5,
respectively) allows approximately 5% to 10% of the UV optical
energy emitted by the LED to be transmitted; i.e., 5%-10% of the
optical energy at UV wavelengths passes through the green phosphor
layer unconverted. This demonstrates that the resulting conversion
efficiency (in this experiment, PCE), of the device can be
optimized by controlling the thickness of the luminescence
conversion layer (in this experiment, green phosphor). The data
plotted in FIG. 14B are extracted from Table 1 below to illustrate
that PCE and UV power after phosphor conversion have a significant
correlation. FIG. 14B demonstrates that, in this example, PCE has a
maximum value when the UV power after phosphor is about 11 mW where
the transmittance is 7.5%.
TABLE-US-00001 TABLE 1 Before After phosphor Transmit- Phosphor
phosphor UV Green PCE tance thickness UV (mW) (mW) (mW) (%) (%)
(.mu.m) Sample 1 149 4.3 67 46.3 2.9 226 Sample 2 145 4.6 74 52.7
3.2 224 Sample 3 148 7.5 91.3 65 5 190 Sample 4 148 11.1 106.8 78
7.5 153 Sample 5 147 14.6 88 66.5 10 108
[0149] In this manner, the devices, systems and methods in
accordance with the present invention provide for high color
repeatability in the resulting LED devices, while reducing the
amount of luminescence conversion material needed, thereby reducing
fabrication costs. In particular, the transmittance and conversion
efficiency of the resulting LED device can be optimized by
accurately controlling a thickness of a luminescence conversion
material layer present in the device, where wavelength conversion
of optical energy occurs. The thickness of the luminescence
conversion material layer is accurately controlled by applying the
luminescence conversion material to a top surface of a soft-cured
first encapsulation layer that covers the underlying LED, and
optionally, by applying a controlled pressure for pressing the
applied luminescence conversion material into the top surface.
Experimental results demonstrate a close correlation between the
thickness of the luminescence conversion material layer and the
resulting transmittance and conversion efficiency of the resulting
LED device.
[0150] While embodiments of the invention have been particularly
shown and described with references to preferred embodiments
thereof, it will be understood by those skilled in the art that
various changes in form and details may be made herein without
departing from the spirit and scope of the invention as defined by
the appended claims.
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