U.S. patent application number 16/042660 was filed with the patent office on 2018-11-15 for wavelength converted light emitting device with small source size.
This patent application is currently assigned to Lumileds LLC. The applicant listed for this patent is Lumileds LLC. Invention is credited to Grigoriy Basin, Hideo Kageyama, Brendan Jude Moran.
Application Number | 20180331261 16/042660 |
Document ID | / |
Family ID | 53434411 |
Filed Date | 2018-11-15 |
United States Patent
Application |
20180331261 |
Kind Code |
A1 |
Basin; Grigoriy ; et
al. |
November 15, 2018 |
WAVELENGTH CONVERTED LIGHT EMITTING DEVICE WITH SMALL SOURCE
SIZE
Abstract
A lighting structure according to embodiments of the invention
includes a semiconductor light emitting device and a flat
wavelength converting element attached to the semiconductor light
emitting device. The flat wavelength converting element includes a
wavelength converting layer for absorbing light emitted by the
semiconductor light emitting device and emitting light of a
different wavelength. The flat wavelength converting element
further includes a transparent layer. The wavelength converting
layer is formed on the transparent layer.
Inventors: |
Basin; Grigoriy; (San
Francisco, CA) ; Moran; Brendan Jude; (San Jose,
CA) ; Kageyama; Hideo; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumileds LLC |
San Jose |
CA |
US |
|
|
Assignee: |
Lumileds LLC
San Jose
CA
|
Family ID: |
53434411 |
Appl. No.: |
16/042660 |
Filed: |
July 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15318143 |
Dec 12, 2016 |
10090444 |
|
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PCT/IB2015/054261 |
Jun 5, 2015 |
|
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16042660 |
|
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62014288 |
Jun 19, 2014 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/60 20130101;
H01L 2224/97 20130101; H01L 33/505 20130101; H01L 2224/16225
20130101; H01L 2933/0041 20130101 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/60 20060101 H01L033/60 |
Claims
1. A lighting structure comprising: a semiconductor light emitting
device deposited on a die; a substantially flat wavelength
converting element attached to the semiconductor light emitting
device, an area of a first surface of the wavelength converting
element facing the semiconductor light emitting device being
greater or similar to an area of a first surface of the
semiconductor light emitting device, the substantially flat
wavelength converting element comprising a wavelength converting
layer, and the area of the first surface of the wavelength
converting element being substantially the same as the area of a
first surface of the die; and a reflective material in direct
contact with a side of the semiconductor light emitting device and
a portion of the first surface of the wavelength converting element
extending beyond the first surface of the semiconductor light
emitting device.
2. The lighting structure of claim 1 wherein the area of the first
surface of the substantially flat wavelength converting element is
no more than 150% of an area of a first surface of the
semiconductor light emitting device.
3. The lighting structure of claim 1 wherein the wavelength
converting element further comprises a transparent layer, the
wavelength converting layer is deposited on the transparent layer,
the transparent layer comprising glass and the wavelength
converting layer comprising phosphor mixed with a transparent
material and laminated on the glass.
4. The lighting structure of claim 1 wherein a length that the
wavelength converting element extends beyond an edge of the
semiconductor light emitting device is no more than 30 .mu.m.
5. The lighting structure of claim 1, wherein the die is one of a
plurality of wafer die on a semiconductor light emitting device
wafer.
6. The lighting structure of claim 5, wherein the semiconductor
light emitting device wafer is sigulated to separate the die from
the plurality of wafer die.
7. The lighting structure of claim 1, wherein the reflective
material comprises TiO.sub.2.
8. The lighting structure of claim 7, wherein the TiO.sub.2 is
deposited in a silicone material.
9. A method comprising: forming a wavelength converting element
comprising a wavelength converting layer; after said forming,
attaching the wavelength converting element to a wafer of
semiconductor light emitting devices; after said attaching, dicing
the wavelength converting element and the wafer of semiconductor
light emitting devices to form a plurality of lighting elements;
after said dicing, disposing the plurality of lighting elements on
a handling substrate; and disposing a reflective material between
the plurality of lighting elements.
10. The method of claim 9 wherein forming a wavelength converting
element comprises laminating a wavelength converting layer on a
glass layer.
11. The method of claim 9, further comprising depositing the
wavelength converting layer on a transparent layer.
12. The method of claim 11, further comprising removing the
transparent layer after said attaching.
13. A method comprising: forming a wavelength converting element
comprising a wavelength converting layer, the wavelength converting
element being rigid; after said forming, attaching the wavelength
converting element to a plurality of diced semiconductor light
emitting devices disposed on a first handling substrate; after said
attaching, dicing the wavelength converting element to form a
plurality of lighting elements, after said dicing, disposing the
plurality of lighting elements on a second handling substrate; and
disposing a reflective material between the plurality of lighting
elements.
14. The method of claim 13 wherein the wavelength converting layer
is disposed on a transparent layer.
15. The method of claim 14 wherein forming the wavelength
converting element comprises laminating the wavelength converting
layer on the transparent layer.
16. The method of claim 14 further comprising removing the
transparent layer after said dicing.
17. The method of claim 16 wherein: the wavelength converting
element comprises a thermal release layer disposed between the
wavelength converting layer and the transparent layer; and removing
the transparent layer comprises removing by thermal release.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/318,143, filed Dec. 12, 2016, which is a
.sctn. 371 application of International Application No.
PCT/IB2015/054261, filed Jun. 5, 2015, which claims the benefit of
U.S. Provisional Application No. 62/014,288, filed Jun. 19, 2014,
which are incorporated by reference as if fully set forth.
FIELD OF INVENTION
[0002] The present invention relates to a wavelength converted
semiconductor light emitting device.
BACKGROUND
[0003] Semiconductor light-emitting devices including light
emitting diodes (LEDs), resonant cavity light emitting diodes
(RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting
lasers are among the most efficient light sources currently
available. Materials systems currently of interest in the
manufacture of high-brightness light emitting devices capable of
operation across the visible spectrum include Group III-V
semiconductors, particularly binary, ternary, and quaternary alloys
of gallium, aluminum, indium, and nitrogen, also referred to as
III-nitride materials. Typically, III-nitride light emitting
devices are fabricated by epitaxially growing a stack of
semiconductor layers of different compositions and dopant
concentrations on a sapphire, silicon carbide, III-nitride, or
other suitable substrate by metal-organic chemical vapor deposition
(MOCVD), molecular beam epitaxy (MBE), or other epitaxial
techniques. The stack often includes one or more n-type layers
doped with, for example, Si, formed over the substrate, one or more
light emitting layers in an active region formed over the n-type
layer or layers, and one or more p-type layers doped with, for
example, Mg, formed over the active region. Electrical contacts are
formed on the n- and p-type regions.
[0004] FIGS. 1A, 1B, 1C, and 1D illustrate a method of forming a
phosphor-converted LED, described in more detail in US
2013/0187174. In FIG. 1A, a base 410 is provided and light emitting
elements (LEEs) 210 are placed on or adhered to base 410 with
contacts 220 adjacent to base 410. The LEEs 210 have a spacing 405
between adjacent elements. Base 410 may also be referred to as a
"mold substrate." In one embodiment, base 410 includes or consists
essentially of an adhesive film or tape. In some embodiments, base
410 includes or consists essentially of a material to which has a
relatively low adhesion to phosphor 230, that is, it permits
removal of cured phosphor 230 from base 410.
[0005] In FIG. 1B, barriers 450 are formed. Barriers 450 are shown
as perpendicular or substantially perpendicular to a surface 435.
The spacing 405 between adjacent LEEs 210 may be adjusted to
control the width of cured phosphor 230 around the sides of LEEs
210 as shown in FIG. 1D. Spacing 405 between LEEs 210 is
approximately determined by the sum of twice the desired sidewall
thickness of the phosphor and the kerf (where the kerf is the width
of the region removed during the singulation process of finished
dies 200, for example identified as kerf 470 in FIG. 1D. The
thickness of cured phosphor 230 over the LEEs 210 may be controlled
by controlling a thickness 425 of phosphor 420 that is formed or
dispensed as shown in FIG. 1B. Thickness 260 of cured phosphor 230
over LEE 210 is given approximately by the thickness of dispensed
phosphor, 425 less the thickness 445 of the LEE.
[0006] Phosphor 420 includes or consists essentially of a phosphor
and a binder. Phosphor 420 is contained or bounded by surface 435
of base 410 and optional sides or barriers 450. Phosphor 420 has a
bottom surface or face 460 and a top surface or face 440, which are
substantially parallel to each other.
[0007] Phosphor 420 is then cured, producing cured phosphor 230 as
shown in FIG. 1C.
[0008] In FIG. 1D, white dies 200 are separated or singulated from
the structure shown in FIG. 1D. White dies 200 may have a size
ranging from about 0.25 mm to about 5 mm.
SUMMARY
[0009] It is an object of the invention to provide a wavelength
converted semiconductor light emitting device with a small source
size.
[0010] A lighting structure according to embodiments of the
invention includes a semiconductor light emitting device and a flat
wavelength converting element attached to the semiconductor light
emitting device. The flat wavelength converting element includes a
wavelength converting layer for absorbing light emitted by the
semiconductor light emitting device and emitting light of a
different wavelength. The flat wavelength converting element
further includes a transparent layer. The wavelength converting
layer is formed on the transparent layer.
[0011] A method according to embodiments of the invention includes
forming a wavelength converting element including a wavelength
converting layer disposed on a transparent layer. The wavelength
converting element is then attached to a wafer of semiconductor
light emitting devices. The wavelength converting element and the
wafer of semiconductor light emitting devices are then diced to
form a plurality of lighting elements. The plurality of lighting
elements are then disposed on a handling substrate. A reflective
material is disposed between the plurality of lighting
elements.
[0012] A method according to embodiments of the invention includes
forming a wavelength converting element, the wavelength converting
element including a wavelength converting layer disposed on a
transparent layer. The wavelength converting element is then
attached to a plurality of diced semiconductor light emitting
devices disposed on a handling substrate. The wavelength converting
element is then diced to form a plurality of lighting elements.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0013] FIGS. 1A, 1B, 1C, and 1D illustrate a method of forming a
phosphor-converted light emitting element.
[0014] FIG. 2 illustrates one example of a III-nitride LED.
[0015] FIG. 3 illustrates a wavelength converting layer disposed on
a transparent layer.
[0016] FIG. 4 illustrates the structure of FIG. 3 attached to a
wafer of LEDs.
[0017] FIG. 5 illustrates the structure of FIG. 4 after dicing the
wafer into individual LEDs, attaching the LEDs to a handling
substrate, and forming a reflective material over the LEDs.
[0018] FIG. 6 illustrates the structure of FIG. 5 after removing
excess reflective material.
[0019] FIG. 7 illustrates individual LEDs disposed on a handling
substrate with a wavelength converting layer disposed on a
transparent layer attached to the LEDs.
[0020] FIG. 8 illustrates singulating two of the LEDs illustrated
in FIG. 7.
[0021] FIG. 9 illustrates the singulated LEDs of FIG. 7 disposed on
a handling substrate, with a reflective material disposed over the
LEDs.
[0022] FIG. 10 illustrates the structure of FIG. 9 after removing
excess reflective material.
[0023] FIG. 11 illustrates the structure of FIG. 10 after removing
the substrate from the wavelength converting layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0024] Because the phosphor extends over the edges of the LEE in
FIG. 1D, the devices illustrated in FIG. 1D have a larger source
size than the light emitting diode without the phosphor layer.
Because of the large source size, the devices illustrated in FIG.
1D may be less bright than the same amount of light emitted in a
smaller source size. The large source size makes the devices
illustrated in FIG. 1D undesirable in some applications.
[0025] Embodiments of the invention include wavelength converted
devices with a relatively small source size, which may be
inexpensive to manufacture.
[0026] Though in the examples below the semiconductor light
emitting device are III-nitride LEDs that emits blue or UV light,
semiconductor light emitting devices besides LEDs such as laser
diodes and semiconductor light emitting devices made from other
materials systems such as other III-V materials, III-phosphide,
III-arsenide, II-VI materials, ZnO, or Si-based materials may be
used.
[0027] FIG. 2 illustrates a III-nitride LED 1 that may be used in
embodiments of the present invention. Any suitable semiconductor
light emitting device may be used and embodiments of the invention
are not limited to the device illustrated in FIG. 2. The device of
FIG. 2 is formed by growing a III-nitride semiconductor structure
on a growth substrate 10 as is known in the art. The growth
substrate is often sapphire but may be any suitable substrate such
as, for example, SiC, Si, GaN, or a composite substrate. A surface
of the growth substrate on which the III-nitride semiconductor
structure is grown may be patterned, roughened, or textured before
growth, which may improve light extraction from the device. A
surface of the growth substrate opposite the growth surface (i.e.
the surface through which a majority of light is extracted in a
flip chip configuration) may be patterned, roughened or textured
before or after growth, which may improve light extraction from the
device.
[0028] The semiconductor structure includes a light emitting or
active region sandwiched between n- and p-type regions. An n-type
region 16 may be grown first and may include multiple layers of
different compositions and dopant concentration including, for
example, preparation layers such as buffer layers or nucleation
layers, and/or layers designed to facilitate removal of the growth
substrate, which may be n-type or not intentionally doped, and n-
or even p-type device layers designed for particular optical,
material, or electrical properties desirable for the light emitting
region to efficiently emit light. A light emitting or active region
18 is grown over the n-type region. Examples of suitable light
emitting regions include a single thick or thin light emitting
layer, or a multiple quantum well light emitting region including
multiple thin or thick light emitting layers separated by barrier
layers. A p-type region 20 may then be grown over the light
emitting region. Like the n-type region, the p-type region may
include multiple layers of different composition, thickness, and
dopant concentration, including layers that are not intentionally
doped, or n-type layers.
[0029] After growth, a p-contact is formed on the surface of the
p-type region. The p-contact 21 often includes multiple conductive
layers such as a reflective metal and a guard metal which may
prevent or reduce electromigration of the reflective metal. The
reflective metal is often silver but any suitable material or
materials may be used. After forming the p-contact 21, a portion of
the p-contact 21, the p-type region 20, and the active region 18 is
removed to expose a portion of the n-type region 16 on which an
n-contact 22 is formed. The n- and p-contacts 22 and 21 are
electrically isolated from each other by a gap 25 which may be
filled with a dielectric such as an oxide of silicon or any other
suitable material. Multiple re-contact vias may be formed; the n-
and p-contacts 22 and 21 are not limited to the arrangement
illustrated in FIG. 2. The n- and p-contacts may be redistributed
to form bond pads with a dielectric/metal stack, as is known in the
art.
[0030] In order to form electrical connections to the LED 1, one or
more interconnects 26 and 28 are formed on or electrically
connected to the n- and p-contacts 22 and 21. Interconnect 26 is
electrically connected to n-contact 22 in FIG. 2. Interconnect 28
is electrically connected to p-contact 21. Interconnects 26 and 28
are electrically isolated from the n- and p-contacts 22 and 21 and
from each other by dielectric layer 24 and gap 27. Interconnects 26
and 28 may be, for example, solder, stud bumps, gold layers, or any
other suitable structure. The semiconductor structure, n- and
p-contacts 22 and 21, and interconnects 26 and 28 are shown in the
following figures as LED structure 12.
[0031] The substrate 10 may be thinned or entirely removed. In some
embodiments, the surface of substrate 10 exposed by thinning is
patterned, textured, or roughened to improve light extraction.
[0032] Many individual LEDs are formed on a single wafer then diced
from a wafer of devices. Any suitable device may be used. The
invention is not limited to the particular LED illustrated in FIG.
2. The combined thickness of substrate 10 and LED structure 12 may
be at least 50 .mu.m in some embodiments, no more than 500 .mu.m in
some embodiments, at least 100 .mu.m in some embodiments, and no
more than 250 .mu.m in some embodiments. The substrate 10 may be no
more than 250 .mu.m thick in some embodiments, no more than 150
.mu.m thick in some embodiments, and at least 100 .mu.m thick in
some embodiments.
[0033] Separate from the LEDs, a wavelength converting element is
formed, as illustrated in FIG. 3. The wavelength converting element
includes a support substrate 30 and a wavelength converting layer
32. The wavelength converting element is formed on a wafer scale,
meaning that the wavelength converting element illustrated in FIG.
3 can be thought of as a wafer of many individual wavelength
converting elements.
[0034] In some embodiments, the support substrate 30 becomes part
of the light emitting device. In these embodiments, the support
substrate 30 may be transparent to the light emitted by the LED
and/or the light emitted by the phosphor. The support substrate may
also be sufficiently robust to withstand any processing steps that
occur after attaching the wavelength converting element to an LED
and to withstand the operating conditions of the light emitting
device, and may be formed of a material that is optically suitable
for the light emitting device. The support substrate 30 may be, for
example, glass, silicone, polymer, polyethylene terephthalate
(PET), or any other suitable material.
[0035] In some embodiments, the support substrate 30 is removed,
and does not become part of the light emitting device. In these
embodiments, the support substrate 30 material is selected for cost
and suitability for the processing steps to which the support
substrate 30 is subjected. If the support substrate 30 is removed
after processing, the support substrate need not be
transparent.
[0036] The wavelength converting layer 32 includes a wavelength
converting material which may be, for example, conventional
phosphors, organic phosphors, quantum dots, organic semiconductors,
II-VI or III-V semiconductors, II-VI or III-V semiconductor quantum
dots or nanocrystals, dyes, polymers, or other materials that
luminesce. The wavelength converting material absorbs light emitted
by the LED and emits light of one or more different wavelengths.
Unconverted light emitted by the LED is often part of the final
spectrum of light extracted from the structure, though it need not
be. Examples of common combinations include a blue-emitting LED
combined with a yellow-emitting wavelength converting material, a
blue-emitting LED combined with green- and red-emitting wavelength
converting materials, a UV-emitting LED combined with blue- and
yellow-emitting wavelength converting materials, and a UV-emitting
LED combined with blue-, green-, and red-emitting wavelength
converting materials. Wavelength converting materials emitting
other colors of light may be added to tailor the spectrum of light
extracted from the structure.
[0037] The wavelength converting layer 32 may include a transparent
material such as silicone that is mixed with the wavelength
converting material. The wavelength converting layer 32 is formed
and attached to the support substrate 30 by any suitable technique.
In some embodiments, a wavelength converting layer 32 that is a
wavelength converting material mixed with a transparent material is
dispensed, screen printed, stenciled, spin-casted, laminated,
molded or otherwise formed on a glass support substrate 30. The
wavelength converting layer 32 may be formed by a process that
includes curing, for example by exposing the wavelength converting
layer to light and/or to elevated temperature. For example, a
laminated wavelength converting layer 32 may be cured at a
temperature greater than 120.degree. C. in some embodiments and
less than 180.degree. C. in some embodiments. In some embodiments
the wavelength converting layer 32 is partially cured when it is
disposed on the support substrate, and partially cured during a
later processing step such as, for example, when it is attached to
light emitting devices.
[0038] The wavelength converting layer 32 may have a thickness of
at least 30 .mu.m in some embodiments, no more than 100 .mu.m in
some embodiments, at least 50 .mu.m in some embodiments, and no
more than 80 .mu.m in some embodiments. The support substrate 30
may be thinner than the wavelength converting layer 32 in some
embodiments, though this is not required. A transparent support
substrate 30 such as glass may have a thickness of at least 10
.mu.m in some embodiments, at least 20 .mu.m in some embodiments,
no more than 200 .mu.m in some embodiments, no more than 150 .mu.m
in some embodiments, no more than 60 .mu.m in some embodiments, and
no more than 50 .mu.m in some embodiments.
[0039] In FIG. 4, the wavelength converting element illustrated in
FIG. 3 is attached to a wafer of LEDs before the LED wafer is
diced. The surface of the wavelength converting layer 32 opposite
the support substrate 30 is attached to the surface of substrate 10
opposite the LED structures 12A-12F. The wavelength converting
element may be attached to the LED wafer by any suitable technique,
such as gluing with silicone or any other suitable adhesive, or
heating the wavelength converting element such that the transparent
material in the wavelength converting layer 32 adheres to the
substrate 10.
[0040] The structure illustrated in FIG. 4 is then diced into
individual LEDs, or groups of LEDs. The structure illustrated in
FIG. 4 is diced for example by cutting through the support
substrate 30, the wavelength converting layer 32, the substrate 10,
and a portion of the LED structures 12A-12F in the regions 34
illustrated in FIG. 4. The layers may be cut together in a single
cutting step, or individual layers may be separately cut in
multiple cutting steps. For example, the substrate 10 and LED
structure 12 may be cut by, for example, scribing and breaking,
before or after the support substrate 30 and wavelength converting
layer 32 are cut by, for example, sawing. Any suitable cutting
technique(s) may be used such as, for example, sawing, laser
scribing, scribe-and-break, blade cutting, or any other suitable
process. Though only six individual LEDs are illustrated in FIG. 4,
an LED wafer may include many more individual LEDs.
[0041] In FIG. 5, the LEDs that were diced in FIG. 4 are placed on
a handling substrate 40. Only a portion of a single handling
substrate 40 including three LEDs 38A, 38B, and 38C is illustrated
in FIG. 5. The processes illustrated in FIGS. 5 and 6 may be
undertaken at a scale where hundreds or thousands of LEDs are
disposed on a single handling substrate 40. The handling substrate
40 is any suitable structure from which the LEDs may be later
removed, such as, for example, wafer handling tape. The LEDs may be
spaced at least 100 .mu.m apart in some embodiments, at least 150
.mu.m apart in some embodiments, at least 200 .mu.m apart in some
embodiments, and no more than 500 .mu.m apart in some
embodiments.
[0042] A reflective material 36 is disposed over LEDs 38A, 38B, and
38C. Reflective material may be, for example, white or reflective
particles such as TiO2 disposed in a transparent material. The
reflective particles and the transparent material may form a
contrast in index of refraction, which scatters and/or reflects
light. The reflective material may be formed by any suitable
technique; for example the reflective material may be molded,
dispensed, laminated, or otherwise disposed over the LEDs.
[0043] In some embodiments, as illustrated in FIG. 5, excessive 42
reflective material 36 is formed over the tops of LEDs 38A, 38B,
and 38C. The excessive material 42 illustrated in FIG. 5 may be
removed, as illustrated in FIG. 6. The excessive material 42 may be
removed by any suitable technique, including dry bead blasting, wet
bead blasting, grinding, polishing, mechanical techniques, or
etching. After the excessive material is removed, the tops 46 of
LEDs 38A, 38B, and 38C are exposed. The top surface 46 is a surface
of support substrate 30 opposite the wavelength converting layer
32. In some embodiments, the technique for removing excessive
material 42 is selected to roughen, polish, texture, or pattern the
top surface 46, for example to improve light extraction from the
device. Alternatively, the top surface may be roughened, polished,
textured, or patterned in a separate processing step.
[0044] In some embodiments, after removing the excessive material
42 shown in FIG. 5, the top surface 48 of reflective material 36
between LEDs is at the same level as the top surface of LEDs 38A,
38B, 38C. In some embodiments, as illustrated in FIG. 6, after
removing the excessive reflective material, the top surface 48 of
reflective material 36 between LEDs is at a different level than
the top surface of LEDs 38A, 38B, 38C. In particular, the top
surface 48 of reflective material 36 between LEDs may be below the
top surface of LEDs 38A, 38B, 38C. Reducing the thickness of the
reflective material to below the top surface of the LEDs may be
useful, for example, in embodiments as described below where the
support substrate 30 is removed after forming the reflective
material.
[0045] The LEDs may then be separated into individual devices or
groups of devices by cutting the reflective material between LEDs,
for example in regions 50 illustrated in FIG. 6. The LEDs may then
be removed from the handling substrate 40 by any technique suitable
to the particular handling substrate used. Because reflective
material 36 is disposed on the sides of the LED, light is extracted
from the final device primarily through the top surface of the LED
(the surface of the support substrate 30 of the wavelength
converting member in the embodiment illustrated in FIG. 6). The
thickness of the reflective material on the sides of the LEDs after
cutting may be at least 30 .mu.m in some embodiments, at least 50
.mu.m in some embodiments, at least 100 .mu.m in some embodiments,
and no more than 500 .mu.m in some embodiments.
[0046] In some embodiments, as illustrated in FIGS. 7, 8, 9, 10,
and 11, the wavelength converting element wafer illustrated in FIG.
3 is attached to a group of LEDs after the LEDs are separated from
a wafer of LEDs. In these embodiments, the LED wafer is diced
before the wavelength converting element wafer. It may be difficult
to simultaneously dice the wavelength converting element and the
LED wafer, as described above in reference to FIG. 4.
[0047] In FIG. 7, previously diced LEDs are disposed on a handling
substrate 40. Only a portion of a single handling substrate 40
including four LEDs 52A, 52B, 52C, and 52D is illustrated in FIG.
7. The processes illustrated in FIGS. 7-11 may be undertaken at a
scale where hundreds of LEDs are disposed on a single handling
substrate 40. The handling substrate 40 is any suitable structure
from which the LEDs may be later removed, such as, for example,
wafer handling tape.
[0048] A wavelength converting element wafer, as described above in
FIG. 3, is attached to a top surface of the LEDs by any appropriate
material or technique. The wavelength converting element wafer may
be attached such that the wavelength converting layer 32 is
disposed between the LEDs and the support substrate 30, as
illustrated in FIG. 7, though the opposite orientation, where the
support substrate 30 is disposed between the LEDs and the
wavelength converting layer 32, is also possible.
[0049] The wavelength converting element wafer is then cut in
regions 51 to form single devices or groups of devices. Cutting the
wavelength converting element wafer between two LEDs 52A and 52B is
illustrated in FIG. 8.
[0050] In a completed device, the wavelength converting member over
a single LED is preferably as close as possible to the size of the
top surface of the LED, in order to limit the source size and
thereby improve the efficiency of the device. Exemplary LEDs 52A
and 52B are therefore spaced as close together on handling
substrate 40 as possible. The spacing of LEDs 52A and 52B may be
determined by the width of the kerf 56 resulting from cutting the
wavelength converting element, and the tolerance of the wavelength
converting element cutting operation.
[0051] The width of the kerf may vary depending on the cutting
technique used. A kerf 56 formed by, for example, sawing, may be no
more than 75 .mu.m wide in some embodiments, no more than 50 .mu.m
wide in some embodiments, no more than 25 .mu.m wide in some
embodiments, and at least 10 .mu.m wide in some embodiments.
[0052] The spacing 54 between neighboring devices may be no more
than 150 .mu.m in some embodiments, no more than 100 .mu.m in some
embodiments, no more than 50 .mu.m in some embodiments, and at
least 30 .mu.m in some embodiments. The overhang 58, or the length
that the wavelength converting member extends out beyond the LED
after cutting, may be no more than 50 .mu.m in some embodiments, no
more than 30 .mu.m in some embodiments, no more than 20 .mu.m in
some embodiments, and at least 10 .mu.m in some embodiments.
[0053] As illustrated in FIG. 8, the wavelength converting layer 32
over each LED is substantially flat in that it does not extend down
over the sides of the LED. In some embodiments, the area of the
wavelength converting layer is larger than the area of the top
surface of the LED. The area of the wavelength converting layer may
be at least 100% of the area of the top surface of the LED in some
embodiments, at least 110% of the area of the top surface of the
LED in some embodiments, no more than 125% of the area of the top
surface of the LED in some embodiments, no more than 150% of the
area of the top surface of the LED in some embodiments, and no more
than 200% of the area of the top surface of the LED in some
embodiments. In some embodiments, the area of the wavelength
converting layer is the same as the area of the top surface of the
LED, or even slightly smaller than the area of the top surface of
the LED.
[0054] In FIG. 9, after cutting the wavelength converting element
wafer as illustrated in FIG. 8 to form individual LEDs or groups of
LEDs, the LEDs 60A, 60B and 60C are removed from the handling
substrate 40 and placed on a different handling substrate 41. The
different handling substrate 41 may be any suitable material and
may be the same type of handling substrate as handling substrate
40, such as, for example, wafer handling tape.
[0055] Alternatively, the LEDs may be left on the handling
substrate 40 illustrated in FIG. 8, which may be stretched to space
the LEDs further apart. The LEDs in FIG. 9 may be spaced at least
100 .mu.m apart in some embodiments, at least 150 .mu.m apart in
some embodiments, at least 200 .mu.m apart in some embodiments, and
no more than 500 .mu.m apart in some embodiments.
[0056] A reflective material 36 is molded over the LEDs, as
described above in reference to FIG. 5.
[0057] In FIG. 10, excessive reflective material over the tops of
the LEDs is removed, as described above in reference to FIG. 6. As
described above in reference to FIG. 6, after the excessive
material is removed, the tops 64 of LEDs 60A, 60B, and 60C are
exposed. The top surface 64 is a surface of support substrate 30
opposite the wavelength converting layer 32. In some embodiments,
the technique for removing excessive reflective material is
selected to roughen, polish, texture, or pattern the top surface
64, for example to improve light extraction from the device.
[0058] In some embodiments, after removing the excessive reflective
material, the top surface 62 of reflective material 36 between LEDs
is at the same level as the top surface of LEDs 60A, 60B, 60C. In
some embodiments, as illustrated in FIG. 10, after removing the
excessive reflective material, the top surface 62 of reflective
material 36 between LEDs is at a different level than the top
surface 64 of LEDs 60A, 60B, 60C. In particular, the top surface 62
of reflective material 36 between LEDs may be below the top surface
64 of LEDs 60A, 60B, 60C. Reducing the thickness of the reflective
material to below the top surface of the LEDs may be useful, for
example, in embodiments as described below where the support
substrate 30 is removed after forming the reflective material.
[0059] The reflective material may be cut in regions 68 to form
individual LEDs or groups of LEDs, then the devices are removed
from the handling substrate 41, as described above in reference to
FIG. 6.
[0060] FIG. 11 illustrates a device where the support substrate 30
is removed from the wavelength converting layer 32. In the
structure illustrated in FIG. 11, after forming the reflective
material and removing excess reflective material, but before
cutting the reflective material to form individual LEDs or groups
of LEDs illustrated in either FIG. 6 or FIG. 10, the support
substrate 30 is removed from the devices.
[0061] In embodiments where the support substrate is removed, the
support substrate may be a material that is selected for ease of
removal. For example, the support substrate may be PET. A layer of
adhesive such as a silicone adhesive or a thermal release adhesive
may be disposed between the wavelength converting layer 32 and the
support substrate 30 when the wavelength converting element
illustrated in FIG. 3 is formed.
[0062] The support substrate pieces 30 illustrated in FIG. 6 or 10
may be removed by, for example, tape-to-tape transfer, thermal
release, or any other suitable technique, resulting in the
structure illustrated in FIG. 11.
[0063] After removing the support substrate, the top surface 66 of
each of the three LEDs 72A, 72B, and 72C is a surface of the
wavelength converting layer 32. The surface of wavelength
converting layer 32 may be textured, patterned, or roughened, for
example to improve light extraction, during or after the removal of
the support substrate. During the removal of excess reflective
material, the reflective material may be thinned such that after
removing the support substrate, the top surface 66 of the LEDs is
at substantially the same level as the top surface 62 of the
reflective material 36, though this is not required--the top
surfaces 66 of the LEDs may be above or below the top surface 62 of
the reflective material.
[0064] After removing the support substrates, the reflective
material between LEDs is cut in regions 70, to separate the devices
into individual LEDs or groups of LEDs.
[0065] Having described the invention in detail, those skilled in
the art will appreciate that, given the present disclosure,
modifications may be made to the invention without departing from
the spirit of the inventive concept described herein. Therefore, it
is not intended that the scope of the invention be limited to the
specific embodiments illustrated and described.
* * * * *