U.S. patent application number 17/314045 was filed with the patent office on 2021-09-09 for light emitting device.
This patent application is currently assigned to NICHIA CORPORATION. The applicant listed for this patent is NICHIA CORPORATION. Invention is credited to Motokazu YAMADA, Yuichi YAMADA.
Application Number | 20210280754 17/314045 |
Document ID | / |
Family ID | 1000005599038 |
Filed Date | 2021-09-09 |
United States Patent
Application |
20210280754 |
Kind Code |
A1 |
YAMADA; Motokazu ; et
al. |
September 9, 2021 |
LIGHT EMITTING DEVICE
Abstract
A light emitting device includes at least one light emitting
element and at least one light transmissive sealing member. Each of
the at least one light emitting element has a bottom surface
electrically connected to a conductor wiring and a top surface
opposite to the bottom surface in a height direction along a height
of the light emitting device. The at least one light transmissive
sealing member covers the at least one light emitting element,
respectively. Each of the at least one light transmissive sealing
member has a projection shape with a height in the height direction
and a width in a width direction perpendicular to the height
direction. The height is greater than the width. Each of the at
least one light transmissive sealing member includes a wavelength
conversion member.
Inventors: |
YAMADA; Motokazu;
(Tokushima-shi, JP) ; YAMADA; Yuichi; (Anan-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi |
|
JP |
|
|
Assignee: |
NICHIA CORPORATION
Anan-shi
JP
|
Family ID: |
1000005599038 |
Appl. No.: |
17/314045 |
Filed: |
May 7, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
17019352 |
Sep 14, 2020 |
11031532 |
|
|
17314045 |
|
|
|
|
16017953 |
Jun 25, 2018 |
10847688 |
|
|
17019352 |
|
|
|
|
14968897 |
Dec 15, 2015 |
10032969 |
|
|
16017953 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2924/181 20130101;
H01L 2224/16225 20130101; H01L 2224/32225 20130101; H01L 33/54
20130101; H01L 2224/73204 20130101; H01L 33/508 20130101 |
International
Class: |
H01L 33/54 20060101
H01L033/54 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2014 |
JP |
2014-266765 |
Feb 12, 2015 |
JP |
2015-025503 |
Jun 26, 2015 |
JP |
2015-128516 |
Claims
1. A light emitting device comprising: at least one light emitting
element each having a bottom surface electrically connected to a
conductor wiring and a top surface opposite to the bottom surface
in a height direction along a height of the light emitting device;
and at least one light transmissive sealing member covering the at
least one light emitting element, respectively, each of the at
least one light transmissive sealing member having a projection
shape with a height in the height direction and a width in a width
direction perpendicular to the height direction, the height being
greater than the width, each of the at least one light transmissive
sealing member including a wavelength conversion member.
2. The light emitting device according to claim 1, further
comprising: a base on which the conductor wiring is provided,
wherein the at least one light emitting element includes a
plurality of light emitting elements provided on the base, and
wherein the at least one light transmissive sealing member includes
a plurality of light transmissive sealing members covering the
plurality of light emitting elements, respectively.
3. The light emitting device according to claim 2, wherein the
plurality of light emitting elements are arranged in a lattice form
on the base.
4. The light emitting device according to claim 1, wherein each of
the at least one light transmissive sealing member includes a light
diffusion material.
5. The light emitting device according to claim 1, wherein each of
the at least one light transmissive sealing member includes a light
diffusion material.
6. The light emitting device according to claim 1, wherein an
aspect ratio provided by dividing the height by the width is equal
to or higher than 2.0.
7. The light emitting device according to claim 1, wherein the
light emitting device has a light distribution characteristic in
which a center part is darker than a periphery part when light from
the at least one light emitting element is viewed in the light axis
direction.
8. The light emitting device according to claim 1, wherein the
light emitting device has a brightness distribution in which the
center part is darker than the periphery part when light from the
at least one light emitting element is viewed in the light axis
direction.
9. The light emitting device according to claim 1, further
comprising: a base on which the conductor wiring is provided,
wherein the at least one light emitting element is disposed at a
height position of 0.5 mm or less from the base.
10. The light emitting device according to claim 2, wherein a
distance between adjacent light emitting elements among the
plurality of the light emitting elements is equal to or more than
20 mm.
11. The light emitting device according to claim 1, further
comprises a wavelength converter covering the at least one light
emitting element.
12. The light emitting device according to claim 11, wherein a
height of the wavelength converter in the height direction is equal
or less than 1/2 of the height of the projection shape.
13. The light emitting device according to claim 11, wherein the
wavelength converter has a maximum length when the wavelength
converter is viewed from the height direction, and wherein the
maximum length is equal to or less than 4/5 of the width.
14. The light emitting device according to claim 1, wherein the
wavelength conversion member includes a phosphor.
15. The light emitting device according to claim 11, wherein the
wavelength conversion member includes a phosphor, and wherein an
emitted light wavelength of the wavelength converter is longer than
an emitted light wavelength of the phosphor.
16. The light emitting device according to claim 1, wherein a
surface of the projection shape has the smallest curvature at a
light axis of the at least one light emitting element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation application of the
U.S. patent application Ser. No. 17/019,352 filed Sep. 14, 2020,
which is a continuation application of the U.S. patent application
Ser. No. 16/017,953 filed Jun. 25, 2018, which was issued as the
U.S. Pat. No. 10,847,688, which is a divisional application of the
U.S. patent application Ser. No. 14/968,897 filed Dec. 15, 2015,
which was issued as the U.S. Pat. No. 10,032,969, which claims
priority under 35 U. S. C. .sctn. 119 to Japanese Patent
Application No. 2014-266765, filed Dec. 26, 2014, Japanese Patent
Application No. 2015-025503, filed Feb. 12, 2015, and Japanese
Patent Application No. 2015-128516, filed Jun. 26, 2015. The
contents of these applications are incorporated herein by reference
in their entirety.
BACKGROUND
Technical Field
[0002] The present disclosure relates to a light emitting
device.
Discussion of the Background
[0003] Recently, various kinds of electronic components have been
put into practical use, and high performance has been required in
these components. Especially, the electronic component is required
to maintain performance for a long period of time under a severe
usage environment. This requirement is also applied to a light
emitting device using a semiconductor light emitting element such
as a light emitting diode (LED). That is, the performance required
in the light emitting device is getting improved in a general
lighting field and a car-mounted lighting field, and a higher
output (higher brightness) and higher reliability are required.
Furthermore, low-price supply is also required while the high
performance is maintained.
[0004] Especially, as for a backlight used in a liquid crystal
television and a general lighting device, an excellent design is
emphasized, and a thickness is required to be reduced.
[0005] For example, Japanese Unexamined Patent Application
Publication No. 2006-114863 discloses a light emitting diode in
which bat-wing shaped light distribution characteristics are
realized by combining a secondary optical lens and the LED, and a
light can be uniformly diffused in a short irradiation distance, so
that a device can be reduced in thickness.
[0006] In addition, Japanese Unexamined Patent Application
Publication No. 2012-231036 discloses a light emitting diode in
which bat-wing shaped light distribution characteristics are
realized by use of a molded shape.
SUMMARY
[0007] According to a first aspect of the present invention, a
light emitting device includes at least one light emitting element
and at least one light transmissive sealing member. Each of the at
least one light emitting element has a bottom surface electrically
connected to a conductor wiring and a top surface opposite to the
bottom surface in a height direction along a height of the light
emitting device. The at least one light transmissive sealing member
covers the at least one light emitting element, respectively. Each
of the at least one light transmissive sealing member has a
projection shape with a height in the height direction and a width
in a width direction perpendicular to the height direction. The
height is greater than the width. Each of the at least one light
transmissive sealing member includes a wavelength conversion
member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0009] FIGS. 1A and 1B are a top view and a cross-sectional view
showing one example of a light emitting device in an embodiment,
respectively;
[0010] FIG. 2 is a view showing a light distribution characteristic
of the light emitting device in the embodiment;
[0011] FIG. 3 is a cross-sectional view showing one example of a
light emitting device in an embodiment;
[0012] FIG. 4 is a cross-sectional view showing one example of a
light emitting device in an embodiment;
[0013] FIG. 5 is a cross-sectional view showing one example of a
light emitting device in an embodiment;
[0014] FIG. 6 is a top view showing one example of a light emitting
device in an embodiment;
[0015] FIGS. 7A to 7C are views showing shapes of sealing members
in light emitting devices in Examples 3 to 5, respectively;
[0016] FIG. 8 is a view showing light distribution characteristics
of the light emitting devices in Examples 3 to 5;
[0017] FIG. 9 is a view showing brightness distributions of the
light emitting devices in Examples 3 to 5; and
[0018] FIGS. 10A to 10C are views of the brightness distributions
in Examples 3 to 5, respectively.
DESCRIPTION OF THE EMBODIMENTS
[0019] The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various
drawings.
[0020] Hereinafter, the embodiments of the present invention will
be described with reference to the drawings. However, light
emitting devices which will be described below are only provided to
specify a technical idea, and the embodiments of the present
invention is not limited to the following light emitting devices
unless otherwise stated. In addition, the contents described in one
embodiment and one example may be applied to another embodiment and
another example.
[0021] Furthermore, in the following description, the same name or
the same reference represents the same or similar member, so that a
detailed description is appropriately omitted. In addition, as for
each component in the embodiments of the present invention, a
plurality of components may be composed of the same member and one
member may serve as the plurality of components, or a function of
one member may be shared with a plurality of members.
First Embodiment
[0022] FIGS. 1A and 1B are schematic structure diagrams showing one
example of a light emitting device in the first embodiment, in
which FIG. 1A is a top view, and FIG. 1B is a cross-sectional view
taken along a line I-I in FIG. 1A.
[0023] As shown in FIGS. 1A and 1B, in this embodiment, a light
emitting element 105 is mounted on a base member 101 by flip-chip
bonding so as to be connected to a pair of conductor wirings 102
provided on a surface of the base member through a connection
member 103. An upper surface of the conductor wiring 102 is
partially electrically connected to the light emitting element 105,
and this portion is exposed from an insulating member 104.
[0024] An underfill 106 is formed under the light emitting element
105 (between a lower surface of the light emitting element 105 and
the base member 101) and around the light emitting element 105, and
a sealing member 108 containing a light diffusion material is
formed on the light emitting element 105.
[0025] The sealing member 108 has a projection shape (including
roughly long semi-spherical shape, roughly circular cone shape,
roughly circular column shape, and mushroom shape), in which a
height A in a direction of a light axis (L) is greater than a width
C of a bottom surface of the sealing member 108. In addition, a
vertical line passing through a center of the light emitting
element 105 is referred to as the light axis L in the description
of this specification. Due to this configuration, a light emitted
from the light emitting element 105 is diffused by the light
diffusion material, and an intensity of the light emitted from the
light emitting device 100 is roughly proportional to an apparent
area ratio of the sealing member 108. As a result, bat-wing shaped
light distribution characteristics can be obtained as shown in FIG.
2. That is, a light emitting device 100 in this embodiment shows
the light distribution characteristics in which a center part is
darker than a periphery part when the light from the light emitting
element 105 is viewed from the light axis direction.
[0026] An outer shape of the sealing member 108 in a top view is a
substantially circular or substantially elliptical shape. Here, in
the case of the substantially elliptical shape, a radius B of the
bottom surface has a long radius and a short radius, and in this
specification, the short radius is defined as the radius B. In the
case of the substantially circular shape, the substantially
circular bottom surface has a diameter that is defined as the width
C of the substantially circular bottom surface of the sealing
member 108. In the case of the substantially elliptical shape, the
substantially ellipsoidal bottom surface has a length of a short
axis that is defined as the width C of the substantially circular
bottom surface of the sealing member 108 (the width C is equal to
the radius B+the radius B).
[0027] FIG. 2 is a view showing the light distribution
characteristics of the light emitting device in this embodiment. As
shown in FIG. 2, the light emitting device in this embodiment has
the bat-wing shaped light distribution characteristics in which a
relative light intensity is higher at a light distribution angle of
50.degree. to 60.degree. than at an angle of 0.degree. and a light
distribution is wider.
[0028] FIG. 2 shows cases where aspect ratios (A/B) which are
provided by dividing the height A of the sealing member in the
light axis direction by the radius B of the bottom surface of the
sealing member are 2.8, 3.2, and 3.5. It is found that as the
aspect ratio is increased, the relative light intensity is
decreased at around 0.degree. and the light distribution becomes
wide. In order to uniformly diffuse the light, the aspect ratio is
favorably 2.0 or more.
[0029] The light emitting element 105 is directly covered with the
sealing member 108, so that Fresnel loss can be reduced and light
extraction efficiency can be improved, compared with a case where a
secondary lens is used.
[0030] Furthermore, the light emitting element 105 is favorably
disposed at a height of 0.5 mm or less from an upper surface of the
base member.
[0031] Furthermore, according to the light emitting device 100, in
this embodiment, as a concentration of the light diffusion material
is increased, the center part shows a darker brightness
distribution than the periphery part when the light from the light
emitting element 105 is viewed from the light axis direction.
[0032] This is because a light path length in the light axis
direction is longer than a light path length in a direction
vertical to the light axis when viewed from the light emitting
element 105, the light from the light emitting element 105 is
scattered and attenuated.
[0033] Therefore, by adjusting the concentration of the light
diffusion material, a light amount in the light axis direction is
reduced to provide the bat-wing shaped light distribution without
increasing the aspect ratio so much. Thus, a resin amount can be
reduced, and productivity is improved.
[0034] Hereinafter, a preferable embodiment of the light emitting
device 100 in this embodiment will be described.
Base Member 101
[0035] The base member (base) 101 is the member on which the light
emitting element 105 is mounted. The conductor wiring 102 for
supplying a power to the light emitting element 105 is formed on
the surface of the base member 101.
[0036] The base member 101 is made of ceramics, or a resin such as
a phenol resin, an epoxy resin, a polyimide resin, a BT resin, a
polyphthalamide (PPA) resin, and a polyethylene terephthalate (PET)
resin. Among them, in view of low cost and high moldability, an
insulating resin is favorably used. Alternatively, in order to
provide the light emitting device superior in heat resistance and
light resistance, the base member 101 is favorably made of
ceramics.
[0037] The ceramics favorably contains alumina, mullite,
forsterite, glass ceramics, nitride series (such as AlN), or
carbide series (such as SiC). Among them, the ceramics mainly
containing alumina or containing alumina as a main component is
preferable.
[0038] In addition, in the case where the base member 101 is made
of a resin, a glass fiber or an inorganic filler of SiO.sub.2,
TiO.sub.2, Al.sub.2O.sub.3 may be mixed in the resin in order to
improve mechanical strength, to reduce thermal expansion, and to
improve light reflectivity. Furthermore, the base member 101 only
have to insulate and isolate the pair of conductor wirings 102 from
each other, and a metal substrate in which an insulating layer is
formed on a metal member may be used.
Conductor Wiring 102
[0039] The conductor wiring 102 is electrically connected to an
electrode of the light emitting element 105 and is used for
externally supplying a current (power). That is, the conductor
wiring 102 serves as an electrode for externally applying a current
or partially serves as the electrode. In general, the conductor
wiring 102 is composed of at least two separate positive and
negative parts.
[0040] The conductor wiring 102 is formed at least on the upper
surface of the base member on which the light emitting element 105
is mounted. The conductor wiring 102 is made of material which can
be optionally selected, based on the material of the base member
101 and a manufacturing method. For example, in the case where the
base member 101 is made of ceramics, the conductor wiring 102 is
favorably made of high melting temperature material so as to be
endurable against a firing temperature of a ceramic sheet, and a
high melting temperature metal such as tungsten or molybdenum is
favorably used. In addition, the metal may be covered with another
metal such as nickel, gold, or silver, by plating, sputtering, or
vapor deposition.
[0041] Furthermore, in a case where the base member 101 is made of
a glass epoxy resin, the conductor wiring 102 is favorably made of
readily-processable material. Furthermore, in a case where the base
member 101 is made of an injection molded epoxy resin, the
conductor wiring 102 is favorably made of material which can be
readily processed by punching, etching, or bending, and has a
relatively high mechanical strength. As a specific example, the
conductor wiring 102 is composed of a metal of copper, aluminum,
gold, silver, tungsten, iron, or nickel, a metal layer of
iron-nickel alloy, phosphor bronze, copper-iron alloy, or
molybdenum, or lead frame. In addition, its surface may be covered
with another metal material. This material is not limited in
particular, but includes only silver, or alloy containing silver,
copper, gold, aluminum, or rhodium, or a multiple-layer film
containing silver and the above alloy. Furthermore, the metal
material may be formed by sputtering or vapor deposition other than
plating.
Connection Member 103
[0042] The connection member 103 is provided to fix the light
emitting element 105 to the base member 101 or the conductor wiring
102. The connection member 103 is made of an insulating resin or
electrically-conductive material, and in the case of the flip-chip
bonding shown in FIG. 1B, the electrically conductive material is
used. More specifically, the connection member 103 includes Au
alloy, Ag alloy, Pd alloy, In alloy, Pb--Pd alloy, Au--Ga alloy,
Au--Sn alloy, Sn alloy, Sn--Cu alloy, Sn--Cu--Ag alloy, Au--Ge
alloy, Au--Si alloy, Al alloy, Cu--In alloy, or mixture of metal
and flux.
[0043] The connection member 103 may be in the form of liquid,
paste, solid (in the form of sheet, block, powder, or wire), and
the form may be appropriately selected according to a composition
and a shape of the base member. Furthermore, the connection member
103 may be composed of a single member or a combined member.
Insulating Member 104
[0044] The conductor wiring 102 is favorably covered with the
insulating member 104 except for the part to be electrically
connected to the light emitting element 105 or another material.
That is, as shown in each drawing, a resist may be disposed on the
base member to insulate and cover the conductor wiring 102, and the
insulating member 104 can serve as the resist.
[0045] In the case where the insulating member 104 is disposed,
when a white filler is contained similarly to an underfill material
as will be described below, the light can be prevented from being
leaked or absorbed, in addition to the effect of insulating the
conductor wiring 102, so that the light extraction efficiency of
the light emitting device 100 can be improved.
[0046] The insulating member 104 may be made of any material as
long as the material is less likely to absorb the light from the
light emitting element and has an insulating property. For example,
the material includes an epoxy, silicone resin, a modified-silicone
resin, a urethane resin, an oxetane resin, an acrylic resin, a
polycarbonate resin, and a polyimide resin.
Light Emitting Element 105
[0047] The light emitting element 105 mounted on the base member is
not limited in particular, and may be a known element, but in this
embodiment, a light emitting diode is favorably used as the light
emitting element 105.
[0048] The light emitting element 105 may emit any wavelength. For
example, the light emitting element for blue light and green light
may be made of ZnSe, nitride-based semiconductor
(In.sub.xAl.sub.yGa.sub.1-x-yN, 0.ltoreq.x, 0.ltoreq.y,
x+y.ltoreq.1), or GaP. Furthermore, the light emitting element for
red color may be made of GaAlAs, or AlInGaP. Furthermore, a
semiconductor light emitting element made of material other than
the above may be used. A composition, a light color, and a size of
the light emitting element, and the number of the light emitting
elements may be selected according to the purpose.
[0049] The light wavelength can be variously selected depending on
the material and a degree of mixed crystal of the semiconductor
layer. Furthermore, the semiconductor layer may have positive and
negative electrodes on the same surface, or may have positive and
negative electrodes on different surfaces.
[0050] The light emitting element 105 in this embodiment has a
light-transmissive substrate, and semiconductor layers stacked on
the substrate. The semiconductor layers include an n-type
semiconductor layer, an active layer, and a p-type semiconductor
layer formed in this order, and an n-type electrode is formed on
the n-type semiconductor layer, and a p-type electrode is formed on
the p-type semiconductor layer.
[0051] As shown in FIG. 1B, the electrode of the light emitting
element 105 is flip-chip bonded to the conductor wiring 102 on the
surface of the base member 101 through the connection member 103,
and a surface opposite to the surface having the electrode, that
is, a main surface of the light-transmissive substrate serves as a
light extraction surface. The light emitting element 105 is
disposed so as to stride the two insulated and isolated positive
and negative conductor wirings 102 and is electrically connected
and mechanically fixed thereto through the conductive connection
member 103. A method for mounting the light emitting element 105
may use a bump in addition to solder paste. Furthermore, the light
emitting element 105 may be a small packaged element in which the
light emitting element is sealed with a resin or the like, and its
shape and structure is not limited in particular.
[0052] In addition, as will be described below, in the case where
the light emitting device includes a wavelength conversion member,
a nitride semiconductor (In.sub.xAl.sub.yGa.sub.1-x-yN, 0.ltoreq.x,
0.ltoreq.y, x+y.ltoreq.1) that can emit a light having a short
wavelength which can efficiently energize a wavelength conversion
member 109 is favorably adopted.
Underfill 106
[0053] In the case where the light emitting element 105 is
flip-chip bonded, the underfill 106 is favorably formed between the
light emitting element 105 and the base member 101. The underfill
106 contains a filler so that the light from the light emitting
element 105 can be efficiently reflected, and a thermal expansion
rate can be made to approach a thermal expansion rate of the light
emitting element 105.
[0054] The material of the underfill 106 is not limited in
particular as long as it is less likely to absorb the light from
the light emitting element. For example, the material includes an
epoxy resin, a silicone resin, a modified-silicone resin, a
urethane resin, an oxetane resin, an acrylic material, a
polycarbonate resin, and a polyimide resin.
[0055] When the underfill 106 contains the white filler, the light
is more likely to be reflected, and the light extraction efficiency
can be improved. Furthermore, the filler is favorably an inorganic
compound. Here, the "white filler" includes a case where it looks
white when scattered due to a difference in refractive index from a
material around the filler even when the filler is transparent
itself.
[0056] Here, reflectivity of the filler is favorably 50% or more
with respect to the emitted light, and more favorably 70% or more.
Thus, the light extraction efficiency of the light emitting device
100 can be improved. Furthermore, a grain diameter of the filler is
favorably between 1 mu and 10 .mu.m. When the grain diameter of the
filler falls within this range, fluidity of the resin as the
underfill can be improved, and a small space can be surely covered.
In addition, the grain diameter of the filler is favorably between
100 nm and 5 .mu.m, and more favorably between 200 nm and 2 nm. A
shape of the filler may be a spherical shape or scale-like
shape.
[0057] In addition, a side surface of the light emitting element is
favorably prevented from being covered with the underfill by
appropriately selecting and adjusting the grain diameter of the
filler and the material of the underfill. This is because the side
surface of the light emitting element is to be ensured as a light
extraction surface.
Sealing Member 108
[0058] The sealing member 108 is disposed on the base member so as
to cover the light emitting element 105 to protect the light
emitting element 105 from an exterior environment, and to optically
control the light emitted from the light emitting element. In this
embodiment, the light emitting element 105 is directly covered with
the sealing member 108.
[0059] The sealing member 108 may be made of an epoxy resin, a
silicone resin, a mixed resin of these, or light-transmissive
material such as glass. Among them, in view of light resistance and
moldability, the silicone resin is favorably selected.
[0060] The sealing member 108 contains the light diffusion material
to diffuse the light from the light emitting element 105. When the
light diffusion material is contained, the light emitted from the
light emitting element 105 in the direction of the light axis L is
diffused in whole directions by the light diffusion material.
[0061] In addition, the sealing member 108 may contain, in addition
to the light diffusion material, a wavelength conversion member
such as a phosphor which absorbs the light from the light emitting
element 105 and emits a light having a wavelength different from
the light emitted from the light emitting element 105, and a
coloring agent in accordance with a light color emitted from the
light emitting element 105.
[0062] The sealing member 108 can be formed by compression molding
or injection molding to cover the light emitting element 105.
Alternatively, the sealing member 108 may be formed into a shape
shown in each drawing by optimizing viscosity of the material of
the sealing member 108 and dropping or drawing the material on the
light emitting element 105 with a surface tension of the material
itself.
[0063] When the sealing member 108 is formed by the latter method,
the sealing member can be formed by a simpler method without
needing a mold. In addition, when the viscosity of the material of
the sealing member is adjusted in the above method, the desired
viscosity can be obtained by use of the light diffusion material,
the wavelength conversion member, and the coloring agent described
above in addition to the viscosity of the material itself.
Light Diffusion Material
[0064] The light diffusion material includes an oxide such as
SiO.sub.2, Al.sub.2O.sub.3, Al(OH).sub.3, MgCO.sub.3, TiO.sub.2,
ZrO.sub.2, ZnO, Nb.sub.2O.sub.5, MgO, Mg(OH).sub.2, SrO,
In.sub.2O.sub.3, TaO.sub.2, HfO, SeO, Y.sub.2O.sub.3, CaO,
Na.sub.2O, B.sub.2O.sub.3, a nitride such as SiN, AlN, and AlON,
and a fluoride such as MgF.sub.2. These may be used alone or may be
mixed. Alternatively, they may be stacked as multiple layers.
[0065] Furthermore, an organic filler may be used as the light
diffusion material. For example, various particulate resins may be
used. In this case, the various resins include a silicone resin, a
polycarbonate resin, a polyether sulfone resin, a polyalirate
resin, a polytetrafluoroethylene resin, an epoxy resin, a cyanate
resin, a phenol resin, an acrylic resin, a polyimide resin, a
polystyrene resin, a polypropylene resin, a polyvinyl acetal resin,
a polymethylmethacrylate resin, a urethane resin, and a polyester
resin.
[0066] It is favorable that the light diffusion material
substantially does not convert the wavelength of the light from the
light emitting element. Thus, it is possible to prevent color
unevenness in the distributed light which is caused because a
thickness of the layer containing the wavelength conversion member
varies depending on an angle.
[0067] A content amount of the light diffusion material is to be
selected so that the light can be diffused, such as 0.01 wt. % to
30 wt. %, and favorably 2 wt. % to 20 wt. %. In addition, a size of
the light diffusion material is also selected so that the light can
be diffused, such as 0.01 .mu.m to 30 .mu.m, and favorably 0.5
.mu.m to 10 .mu.m. In addition, its shape may be a spherical shape
or scale-like shape, but in order to uniformly diffuse the light,
it is favorably the spherical shape. Here, the concentration of the
light diffusion material varies relatively according to a
difference in refractive index from the sealing member and a
thickness of the sealing member, so that the above values are just
the roughly estimated values.
[0068] For example, the light emitting element itself generally has
the strongest intensity in the light axis direction. Therefore,
when the concentration of the light diffusion material is too low,
the brightness distribution cannot be darker in the center part
than the periphery part when the light from the light emitting
element is viewed from the light axis direction. Thus, the
concentration of the diffusion material is favorably adjusted so
that the center part has the brightness distribution darker than
the periphery part.
[0069] Furthermore, by controlling the concentration of the light
diffusion material in the sealing member 108, the center part can
be darker and the periphery part can be brighter when the light
emitting device 100 is viewed in the light axis direction. Due to
this configuration, by further controlling the light amount in the
light axis direction, the bat-wing shaped light distribution
characteristics can be obtained.
[0070] According to the light emitting device in this embodiment,
the light distribution can be widened without using a secondary
lens, so that in a case where the plurality of the light emitting
elements 105 are disposed on the base member 101, the light can be
uniformly diffused in a short radiation distance even when a
distance between the adjacent light emitting elements is 20 min or
more. Thus, with the plurality of light emitting elements, the
brightness unevenness can be prevented in a surface light source.
Here, the distance between the adjacent light emitting elements
means a shortest distance between the adjacent light emitting
elements 105 as shown by a distance F in FIG. 6.
Second Embodiment
[0071] FIG. 3 is a cross-sectional view showing one example of a
light emitting device in the second embodiment.
[0072] According to this embodiment, a wavelength conversion member
109 is disposed so as to be in contact with a light emitting
element 105, and a sealing member 108 containing a light diffusion
material is formed so as to cover the wavelength conversion member
109.
[0073] As described above, in the case where the sealing member 108
contains the wavelength conversion member as a whole, the color
unevenness in distributed light is caused because the thickness of
the layer containing the wavelength conversion member varies
depending on the angle. Therefore, according to this embodiment,
the wavelength conversion member 109 is formed around the light
emitting element 105, and the sealing member 108 having optical
performance is formed over the wavelength conversion member 109. In
this way, it becomes possible to separately form the region in
which the wavelength is converted (wavelength conversion member
109), and the region in which the optical performance is applied
(sealing member 108), so that while the desired light distribution
characteristic can be obtained, the color unevenness in distributed
light is suppressed.
Wavelength Conversion Member 109
[0074] The wavelength conversion member absorbs the light from the
light emitting element having a light emitting layer made of
nitride-based semiconductor, and converts a wavelength of the light
to a different wavelength. A phosphor material may include a
nitride-based phosphor and an oxynitride-based phosphor which are
mainly activated with lanthanoid such as Eu or Ce. More
specifically, it is favorably at least one selected from the
following elements roughly classified in (D1) to (D3).
[0075] (D1) Phosphors such as alkaline earth halogen apatite,
alkaline earth metal halogen borate, alkaline earth metal
aluminate, alkaline earth metal sulfide, alkaline earth metal
thiogallate, alkaline earth metal silicon nitride, and germinate
which are mainly activated with a lanthanoid such as Eu or a
transition metal such as Mn.
[0076] (D2) Phosphors such as rare earth aluminate, rare earth
silicate, and alkaline earth metal rare earth silicate which are
mainly activated with a lanthanoid such as Ce.
[0077] (D3) Phosphors such as organic or organic complex which are
mainly activated with a lanthanoid such as Eu.
[0078] Among them, a favorable phosphor is a yttrium aluminum
garnet (YAG) phosphor which is a rare earth aluminate phosphor
mainly activated with a lanthanoid such as Ce shown in (D2). The
YAG phosphor is expressed by composition formulas shown in the
following (D21) to (D24).
Y.sub.3Al.sub.5O.sub.12:Ce (D21)
(Y.sub.0.8Gd.sub.0.2).sub.3Al.sub.5O.sub.12:Ce (D22)
Y.sub.3(Al.sub.0.8Ga.sub.0.2).sub.5O.sub.12:Ce (D23)
(Y,Gd).sub.3(Al,Ga).sub.5O.sub.12:Ce (D24)
[0079] In addition, Y may be partially or totally replaced with Tb
or Lu. More specifically, Tb.sub.3Al.sub.5O.sub.12:Ce or
Lu.sub.3Al.sub.5O.sub.12:Ce may be used. Furthermore, other than
the above-described phosphors, a phosphor having the same
performance, action, and effect can be used.
[0080] A grain diameter of the above phosphor is favorably 2.5
.mu.m to 30 .mu.m.
[0081] In addition, the "grain diameter" in this specification
means an average grain diameter, and its value is obtained by an
air permeability method or fisher-subsieve-sizers-No. (F. S. S. S.
No.) (value expressed by D bar (bar above D).
[0082] The wavelength conversion member may be made of light
emitting material called nanocrystal or quantum dot. This material
includes semiconductor materials such as group II-VI, group III-V,
group IV-VI, and group I-III-VI semiconductors. More specifically,
it may be a nanosized high dispersion particles of CdSe, core-shell
CdS.sub.xSe.sub.1-x/ZnS, GaP, InAs, InP, GaN, PbS, PbSe, Cu (In,
Ga)S.sub.2, or Ag (In, Ga)S.sub.2. This quantum dot has a grain
diameter of 1 nm to 100 nm, and favorably 1 nm to 20 nm (having 10
to 50 atoms). With the quantum dots having the above grain
diameter, internal scattering can be prevented, so that the light
can be prevented from scattering in the wavelength conversion
region.
[0083] A light emitting device 200 shown in FIG. 3 may have the
same configuration as the light emitting device 100 in the first
embodiment except that the wavelength conversion member 109 is
provided around the light emitting element 105.
[0084] According to this embodiment, the wavelength conversion
member 109 has a project shape in the direction of the light axis L
similar to the sealing member 108. The wavelength conversion member
109 is disposed so as to be in contact with the exposed surface of
the light emitting element 105 so that the wavelength is converted
between the light emitting element and the sealing member 108.
According to the example shown in FIG. 3, the wavelength conversion
member 109 is formed into a roughly semi-spherical shape to cover
the light emitting element 105.
[0085] An outer shape of the wavelength conversion member 109 is
favorably formed into a circular or ellipsoidal shape when viewed
from the top.
[0086] A height (D) of the wavelength conversion member 109 in the
direction of the light axis (L) is favorably 1/2 or less of a
height (A) of the sealing member 108 in the direction of the light
axis (L). Thus, a thickness of the sealing member 108 can be
ensured, so that color unevenness can be reduced.
[0087] Furthermore, a width (E) of the wavelength conversion member
109 is preferably 4/5 or less of a width (C) of the sealing member
108. Thus, the thickness of the sealing member 108 can be ensured,
so that color unevenness can be reduced. Here, the wavelength
conversion member 109 has a maximum length when the wavelength
converter 109 is viewed from the light axis direction, and the
maximum length of the wavelength conversion member 109 is defined
as the width (E) of the wavelength conversion member 109.
Therefore, in the case of the substantially circular bottom
surface, the maximum length is equal to or less than 4/5 of the
diameter of the substantially circular bottom surface. In the case
of the substantially ellipsoidal bottom surface, the maximum length
is equal to or less than 4/5 of the length of the short axis of the
ellipsoidal bottom surface.
[0088] In addition, the sealing member 108 of the light emitting
device in the second embodiment may contain a wavelength conversion
member. In this case, an emitted light wavelength from the
wavelength conversion member 109 is favorably longer than an
emitted light wavelength from the wavelength conversion member such
as a phosphor in the sealing member 108. Thus, the light whose
wavelength has been converted by the wavelength conversion member
109 can be prevented from being converted again by the wavelength
conversion member contained in the sealing member.
Variation of Second Embodiment
[0089] FIG. 4 is a cross-sectional view showing the variation of
the light emitting device 200 in the second embodiment. A light
emitting device 300 in this variation includes a small-type LED
package 201 including a wavelength conversion member 109 and a
reflection member 203 in a light emitting element 105. More
specifically, the LED package 201 includes the reflection member
203 which covers a side surface and a lower surface of the light
emitting element 105, and the wavelength conversion member 109
which covers an upper surface of the light emitting element 105,
and the LED package 201 is mounted on a base member 101. A terminal
204 of the LED package 201 is electrically connected to a conductor
wiring 102 though a connection member 103.
[0090] In this variation also, similar to the second embodiment, a
region in which wavelength conversion is performed and a region
having optical performance can be separately formed, so that color
unevenness in the distributed light can be prevented. Due to this
configuration, a light source in which chromaticity has been
already selected can be used, so that a product yield regarding
chromaticity can be improved.
Third Embodiment
[0091] FIG. 5 is a cross-sectional view showing one example of a
light emitting device 400 in the third embodiment.
[0092] According to this embodiment, a sealing member 108 is formed
into a shape in which a radius of a region being in contact with a
base member 101 (a bottom surface of the sealing member 108) is
smaller than a maximum radius of the sealing member 108 in a width
direction. The light transmissive sealing member 108 has a maximum
length when the light transmissive sealing member 108 is viewed
from the light axis direction. In the case of the substantially
circular bottom surface, the diameter of the substantially circular
bottom surface is smaller than the maximum length of the light
transmissive sealing member 108. In the case of the substantially
ellipsoidal bottom surface, the light transmissive sealing member
108 has a maximum length in the short axis direction of the
substantially ellipsoidal bottom surface when the light
transmissive sealing member 108 is viewed from the light axis
direction, the length of the short axis of the substantially
ellipsoidal bottom surface is smaller than the maximum length in
the short axis direction of the substantially ellipsoidal bottom
surface. Thus, since the sealing member 108 has a reversely-tapered
part 205 in the vicinity of the base member 101, a light emitted
from the light emitting element in a direction perpendicular to a
light axis (L) changes its direction toward an upper direction of
the base member due to refraction, so that a light amount to
irradiate a whole surface can be increased without being led to the
base member. The light emitting device 400 may have the same
configuration as the light emitting device 100 in the first
embodiment or the light emitting device 200 in the second
embodiment except that the sealing member 108 becomes the
reversely-tapered shape in the vicinity of the base member 101.
[0093] Hereinafter, examples will be described in detail, but the
embodiments of the present invention is not limited to the
examples.
Example 1
[0094] In this example, as shown in FIGS. 1A and 1B, the base
member 101 is made of glass epoxy material, and the conductor
wiring has a thickness of 35 .mu.m and made of Cu.
[0095] The light emitting element is a nitride-based blue LED
having a square shape having one side of 600 .mu.m in a planar
view, and a thickness of 150 .mu.m. The insulating member 104 is
made of epoxy-based white solder resist. The underfill 106 is made
of silicone resin containing 30 wt. % of titanium oxide as a
filler, and the lower surface and side surface of the light
emitting element 105 are covered with the underfill 106. The
sealing member 108 is made of a silicone resin containing 30 wt. %
of SiO.sub.2 filler as a light diffusion material, and as shown in
FIGS. 1A and 1B, and has a roughly long semi-spherical shape and a
circular outer shape in a top view. The height A in the light axis
direction is 5.5 mm, the radius B of the bottom surface of the
sealing member 108 is 1.7 mm, and the aspect ratio (A/B) is
3.2.
[0096] Due to this configuration, the light emitted from the light
emitting element 105 is diffused by the SiO.sub.2 filler serving as
the light diffusion material, so that light intensity from the
light emitting device 100 is roughly proportional to the apparent
area ratio of the sealing member 108. As a result, the light
distribution characteristics can be realized as shown in FIG. 2
when the aspect ratio is 3.2. According to this light distribution,
the relative light intensity is higher at the angles of 50.degree.
to 60.degree. than at the angle of 0.degree., so that the bat-wing
shaped light distribution can be obtained.
Example 2
[0097] As shown in FIG. 3, this example is similar to Example 1
except that the sealing member 108 contains the wavelength
conversion member 109 and is formed around the light emitting
element 105.
[0098] The wavelength conversion member 109 in this example is made
of a silicone resin containing a YAG-based phosphor, and the
sealing member 108 is made of a silicone resin containing a
SiO.sub.2 filler as the light diffusion material.
[0099] Due to this configuration, blue light from the light
emitting element 105 is synthesized with yellow light having a
wavelength converted by the wavelength conversion member 109,
whereby white light is provided, so that the light can be further
diffused in the sealing member 108. As a result, the bat-wing
shaped light distribution having less color unevenness can be
obtained in all directions.
[0100] In Examples 3 to 5, the shape of the sealing member 108 is
changed, and distribution characteristics and brightness
distributions are examined. A light emitting device in Example 3 is
shown in FIG. 7A, a light emitting device in Example 4 is shown in
FIG. 7B, and a light emitting device in Example 5 is shown in FIG.
7C.
[0101] The light emitting devices in Examples 3 to 5 are similar to
each other in that a sealing member 108 has the projection shape in
which a height in a light axis direction is greater than a width of
a bottom surface of the sealing member 108, and contains a light
diffusion material, and an upper surface of the sealing member 108
has a curvature.
[0102] Furthermore, as similar points, a base member is made of
glass epoxy base material, and a conductor wiring has a thickness
of 35 .mu.m and made of Cu. In addition, a light emitting element
is composed of a nitride-based blue LED having a square shape
having one side of 600 .mu.m in a planar view, and a thickness of
150 .mu.m, and an insulating member is made of epoxy-based white
solder resist.
Example 3
[0103] As shown in FIG. 7A, according to the sealing member 108 in
Example 3, the curvature of the upper surface is greater in the
vicinity of the light axis than in other parts, and a roughly
circular cone shape is provided. A side surface of the sealing
member also has a curvature. Namely, a surface of the projection
shape has the smallest curvature at the light axis of the light
emitting element 105. In Example 3, as shown in FIG. 3, the
phosphor layer is formed by applying the phosphor onto the light
emitting element. The phosphor is a YAG-based phosphor, and a white
light emitting device is provided.
Example 4
[0104] As shown in FIG. 7B, according to the sealing member 108 in
Example 4, the curvature of the upper surface is smaller in the
vicinity of the light axis than in other parts, and the upper
surface in the vicinity of the light axis is almost flat.
Furthermore, a side surface of the sealing member is almost
perpendicular to an upper surface of the base member (or an upper
surface of the light emitting element), and a roughly circular
column is provided.
[0105] This shape can be formed as will be described below.
[0106] First, a diffusion material is added to a resin containing a
nano filler and having high thixotropy, and the prepared resin is
applied with a dispenser moved up in a vertical direction (z
direction). Thus, when the dispenser is lifted to a predetermined
height, the lifting is stopped, and the resin is supplied until a
perpendicular cross-sectional surface is formed into a shape close
to a rectangular shape. When a desired shape is formed, the supply
of the resin is stopped, and the resin is cut so as to scrape the
upper surface. Here, although the upper surface of the sealing
member has the curvature in the above example, but the upper
surface may be flat.
[0107] In Example 4, similar to Example 3, a phosphor layer is
formed by applying a phosphor onto the light emitting element, and
a white light emitting device is provided.
Example 5
[0108] As shown in FIG. 7C, the sealing member 108 in Example 5
includes an upper part 10 and a lower part 20, and has a mushroom
shape in which the upper part 10 has a diameter G greater than a
diameter H of the lower part 20. Furthermore, a curvature of the
upper part 10 in the vicinity of the light axis is smaller than a
curvature of other parts, and an upper surface in the vicinity of
the light axis has a roughly flat shape similar to Example 4. The
lower part 20 is formed into a roughly circular column shape having
a surface which is roughly perpendicular to an upper surface of the
base member (or an upper surface of the light emitting element),
and the upper part 10 is formed into a roughly spherical shape.
[0109] Furthermore, as for the side surface of the sealing member,
a diameter is gradually increased from a bottom part, reaches the
greatest point G, and then is gradually reduced toward the upper
surface. Thus, the upper part 10 overlaps with the lower part 20
when the light emitting device is viewed from the top, so that a
periphery of the bottom part of the sealing member having the
highest brightness cannot be directly seen when viewed from the
top, so that uniformity can be improved as will be described
below.
[0110] In Example 5, a phosphor layer is formed in the LED package
201 shown in FIG. 4, and a white light emitting device is
provided.
Light Distribution Characteristics and Brightness Distribution
[0111] FIG. 8 shows the light distribution characteristics of all
of the light emitting devices having the bat-wing shaped light
distributions. The light emitting devices have almost the same
light distribution characteristics except that the light emitting
device in Example 5 is flat in brightness in the vicinity of the
light axis, compared with the light emitting devices in Example 3
and Example 4.
[0112] On the other hand, FIG. 9 shows brightness distributions of
the sealing members 108 and their vicinities when viewed from the
top in the light emitting devices in Examples 3 to 5, and FIGS. 10A
to 10C show in-plane brightness distributions when viewed from the
top, in which FIGS. 10A, 10B, and 10C show the brightness
distributions in Example 3, Example 4, and Example 5,
respectively.
[0113] From the brightness distributions in FIGS. 9 and 10A to 10C,
the light emitting device in Example 5 shows the highest
uniformity. Here, the uniformity means a ratio in brightness
between a darkest part (dark part) in the vicinity of the light
axis, and a brightest part (bright part) (dark part/bright part).
When the value is high, the difference between the bright part and
the dark part is small, which means that the uniformity is high. In
addition, the ratios in brightness in Examples 3, 4, and 5 are
0.157, 0.557, and 0.717, respectively.
[0114] In a case where an irradiation surface such as a light
diffusion plate is very close to the light emitting device, a
brightness distribution of the light emitting device itself appears
other than the light distribution characteristics shown in FIG. 8,
so that in the light emitting device in Example 3, the irradiation
surface has doughnut-shaped bright and dark parts in which a dark
part is provided on the light axis, and a bright part is provided
in its periphery. Meanwhile, in the light emitting devices in
Examples 4 and 5, since the brightness uniformity is high, bright
and dark parts can be prevented from being generated in the
vicinity of the light axis on the irradiation surface.
[0115] From the results of Examples 3 and 4, in the case where the
curvature of the upper surface of the sealing member 108 in the
vicinity of the light axis is smaller than the curvature in other
parts, a difference in light path length between the light axis and
its periphery is small in the sealing member, so that a difference
in light amount passing through in the light axis direction is
small, which improves the uniformity.
[0116] Furthermore, the reason why the uniformity is highest in the
light emitting device in Example 5 is believed that brightest
reflected light from the white solder resist around the bottom part
of the sealing member in Example 4 is blocked and scattered by the
sealing member itself.
[0117] As for the difference in diameter between the upper part 10
and the lower part 20 in this case, the diameter of the upper part
10 is 1.1 times to 2.0 times, and favorably 1.2 times to 1.5 times
longer than the diameter of the lower part 20. Furthermore, since
this diameter ratio varies depending on the aspect ratio and the
light distribution characteristics, it is not limited to the above
range.
[0118] A light emitting device according to an aspect of the
present invention includes a base member having a conductor wiring,
a light emitting element mounted on the base member and
electrically connected to the conductor wiring, and a
light-transmissive sealing member covering the light emitting
element, in which the sealing member has a projection shape in
which a height in a light axis direction is greater than a width of
a bottom surface of the sealing member, and the sealing member
contains a light diffusion material.
[0119] According to the aspect of the present invention, the light
emitting device can realize a bat-wing shaped light distribution in
which color unevenness in distributed light is improved without
using a secondary lens.
[0120] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *