Note: Descriptions are shown in the official language in which they were submitted.
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Description
Title of Invention: LIGHT-EMITTING DEVICE, INTEGRATED
LIGHT-EMITTING DEVICE, AND LIGHT-EMITTING
MODULE
Technical Field
[0001] CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to Japanese Patent Application No. 2015-
200445,
filed on October 8, 2015, and Japanese Patent Application No. 2016-197968,
filed on
October 6, 2016, the disclosures of which are hereby incorporated by reference
in their
entirety.
Background Art
[0002] The present disclosure relates to light-emitting devices, integrated
light-emitting
devices, and light-emitting modules.
[0003] In recent years, various electronic components have been proposed
and put into
practical use, and they are required to exhibit higher performance. In
particular, some
electronic components need to maintain their performance for a long period of
time
under a harsh usage environment. Such requirements can apply to light-emitting
devices using semiconductor light-emitting elements, including a light-
emitting diode
(i.e., LED). That is, in the fields of general illumination and interior and
exterior
lighting for vehicles, the light-emitting devices have been increasingly
required day by
day to demonstrate higher performance, specifically, higher output (i.e.,
higher
luminance) and higher reliability. Furthermore, the light-emitting devices are
requested
to be supplied at low costs while maintaining high performance.
Backlights used in liquid crystal televisions, general lighting devices, and
the like are
developed by focusing on their designs, which leads to a high demand for
thinning.
[0004] For example, Japanese Unexamined Patent Application Publication No.
2008-4948
discloses a light-emitting device in which a reflector is provided on the
upper surface
of a light-emitting element mounted on a submount in a flip-chip manner to
thereby
achieve thinning of the backlight.
[0005] Japanese Unexamined Patent Application Publication No. 2008-4948 can
achieve the
light-emitting device with wide light distribution. However, with further
thinning of
the backlight, a light-emitting device capable of achieving much wider light
dis-
tribution has been required.
Summary of Invention
[0006] Embodiments of the present disclosure have been made in view of the
foregoing cir-
cumstances, and it is an object of the embodiments of the present disclosure
to provide
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a light-emitting device that enables wide light distribution without using a
secondary
lens.
[0007] A light-emitting device according to an embodiment includes: a base
including a
conductive wiring; a light-emitting element mounted on the base and adapted to
emit
light; a light reflective film provided on an upper surface of the light-
emitting element;
and a encapsulant covering the light-emitting element and the light reflective
film, in
which a ratio (H/W) of a height (H) of the encapsulant to a width (W) a bottom
surface
of of the encapsulant is less than 0.5.
[0008] Accordingly, the embodiment of the present disclosure enables the
wide light dis-
tribution without using a secondary lens.
Brief Description of Drawings
[0009] [fig.11Fig. 1 is a cross-sectional view showing an example of a light-
emitting device
according to a first embodiment.
[fig.21Fig. 2 is a diagram showing incident-angle dependence of a light
transmissivity
of a light reflective film in the embodiment.
[fig.31Fig. 3 is a diagram showing a relationship between a wavelength range
of a light
reflective film and an emission wavelength of a light-emitting element in the
light-
emitting device of the embodiment.
[fig.41Fig. 4 is a light distribution characteristic diagram of the light-
emitting device in
the embodiment.
[fig.51Fig. 5 is a light distribution characteristic diagram of a light-
emitting device
using a secondary lens in Comparative Example.
[fig.61Fig. 6A-6I show Experimental Examples according to the embodiment.
[fig.71Fig. 7 is a cross-sectional view showing an example of a light-emitting
module
in a second embodiment.
[fig.8A1Fig. 8A shows an example of a light reflective plate.
[fig.8B1Fig. 8B shows an example of a light reflective plate.
[fig.9A1Fig. 9A shows luminance distribution characteristics of a light-
emitting
module according to Example 2.
[fig.9B1Fig. 9B shows luminance distribution characteristics of a light-
emitting module
according to Example 2.
Description of Embodiments
[0010] Embodiments of the present disclosure will be described below with
reference to the
accompanying drawings as appropriate. A light-emitting device to be described
below
is to embody the technical idea of the present disclosure and is not intended
to limit the
present invention unless otherwise specified. The contents of the description
regarding
one embodiment or example can also be applied to other embodiments and
examples.
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Furthermore, in the description below, the same names or reference characters
denote
the same or similar members, and thus a detailed description thereof will be
omitted as
appropriate. Moreover, regarding each element configuring the present
invention, a
plurality of elements may be formed by the same member, thereby allowing this
one
member to function as these elements. Conversely, the function of one member
can be
shared and achieved by a plurality of members.
[0011] First Embodiment
Fig. 1 is a schematic configuration diagram showing one example of a light-
emitting
device according to a first embodiment.
As shown in Fig. 1, in this embodiment, the light-emitting device includes a
base 101
with conductive wirings 102, and a light-emitting element 105 mounted on the
base
101. The light-emitting element 105 is mounted in a flip-chip manner via
bonding
members 103 to straddle at least a region between a pair of conductive wirings
102
provided at the surface of the base 101. A light reflective film 106 is formed
on a light
extraction surface side of the light-emitting element 105 (i.e., upper surface
of the
light-emitting element 105). At least a part of each conductive wiring may be
provided
with an insulating member 104. A region of the upper surface of the conductive
wiring
102 electrically connected to the light-emitting element 105 is exposed from
the in-
sulating member 104.
[0012] The light transmissivity of the light reflective film 106 is
dependent on an angle of
incidence of the light incident from the light-emitting element 105. Fig. 2 is
a diagram
showing incident-angle dependence of the light transmissivity of the light
reflective
film 106 in this embodiment. The light reflective film 106 hardly allows the
light to
pass therethrough in the direction perpendicular to the upper surface of the
light-
emitting element 105, but increases the amount of the light transmitted as the
angle of
incidence increases relative to the perpendicular direction. Specifically,
when the
incident angle is in a range of -30 to 30 , the light transmissivity is
approximately
10%. When the incident angle becomes smaller than -30 , the light
transmissivity
gradually becomes larger. Further, when the incident angle becomes smaller
than -50 ,
the light transmissivity increases drastically. Likewise, when the incident
angle
becomes larger than 30 , the light transmissivity gradually becomes larger.
Further,
when the incident angle becomes larger than 50 , the light transmissivity
increases
drastically. That is, the light transmissivity of the light reflective film
for said light
increases as an absolute value of an incident angle increases. The formation
of such a
reflective film can achieve the batwing light distribution characteristics
shown in Fig.
4.
The term "batwing light distribution characteristics" as used herein means the
light
distribution characteristics exhibiting a first peak in a first region with a
light dis-
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tribution angle of less than 900, the first peak having a higher intensity
than that at the
light distribution angle of 90 , as well as a second peak in a second region
with a light
distribution angle of more than 90 , the second peak having a higher intensity
than that
at the light distribution angle of 90 .
[0013] The light-emitting element 105 is covered with a light transmissive
encapsulant 108.
The encapsulant 108 is disposed on the base to cover the light-emitting
element 105 in
order to protect the light-emitting element 105 from an external environment
and to
optically control the light output from the light-emitting element. The
encapsulant 108
is formed substantially in the dome shape. The encapsulant 108 covers the
light-
emitting element 105 with the light reflective film 106 disposed thereto, the
surfaces of
the conductive wirings 102 located around the light-emitting element 105, and
connection portions between the light-emitting element 105 including the
bonding
members 103 and the conductive wirings 102. That is, the upper surface and
lateral
surfaces of the light reflective film 106 are in contact with the encapsulant
108, and the
lateral surfaces of the light-emitting element 105 not covered with the light
reflective
film 106 are also in contact with the encapsulant 108. The connection portions
may be
covered with an underfill, not with the encapsulant 108. In this case, the
encapsulant
108 is formed to cover the upper surface of the underfill and the light-
emitting
element. In this embodiment, the light-emitting element 105 is directly
covered with
the encapsulant 108.
[0014] The encapsulant 108 is preferably formed to have a circular or
ellipsoidal outer shape
in the top view, with the ratio of a height (H) of the encapsulant in an
optical-axis
direction to a diameter (width: W) of the encapsulant in the top view set to a
value less
than 0.5. For the encapsulant 108 having the ellipsoidal shape, there are a
major axis
and a minor axis that can be considered as the length of the width, but the
minor axis is
defined as a diameter (W) of the encapsulant 108 in the present specification.
The
upper surface of the encapsulant 108 is formed in a convex curved shape.
With this arrangement, the light emitted from the light-emitting element 105
is
refracted at an interface between the encapsulant 108 and air, which can
achieve the
wider light distribution.
Here, the height (H) of the encapsulant indicates the height from a mounting
surface
for the light-emitting element 105 as shown in Fig. 1. The width (W) of the en-
capsulant indicates its diameter when the encapsulant has a circular bottom
surface as
mentioned above, or alternatively indicates the length of the shortest part
thereof when
the encapsulant has any shape other than the circle.
[0015] Fig. 4 shows an example of changes in the light distribution
characteristics
depending on the presence or absence of the encapsulant 108. In Fig. 4, the
solid line
shows the light distribution characteristic of a light-emitting device 100 in
the first em-
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bodiment. On the other hand, the dotted line shows the light distribution
characteristic
of a light-emitting device fabricated in the same way as in the first
embodiment except
that the encapsulant 108 is not formed.
As can be seen from Fig. 4 according to the light-emitting device in the first
em-
bodiment, the first peak moves in the direction that decreases the light
distribution
angle as well as the second peak moving in the direction that increases the
light dis-
tribution angle, as compared with a light-emitting device without the
encapsulant 108.
Therefore, the light-emitting device in the first embodiment can achieve the
wider light
distribution.
[0016] The use of both the light reflective film 106 and the encapsulant
108 in this way can
achieve the desired light distribution characteristics without using the
secondary lens.
That is, the formation of the light reflective film 106 can reduce the
luminance directly
above the light-emitting element 105, while the encapsulant 108 can
concentrate on
widening the distribution of the light from the light-emitting element 105,
which
enables significant downsizing of the encapsulant with a lens function.
In other words, conventionally, reduction in luminance directly above the
light-
emitting element while widening the light distribution is possible only by
adjusting a
height of the encapsulant, as a result, the height of the encapsulant must be
increased
In contrast, the light-emitting device in this embodiment includes the light
reflective
film 106 having reduced luminance directly above the light-emitting element
105,
thereby achieving the batwing light distribution characteristics. Thereby, the
en-
capsulant 108 can be configured to focus on the function of widening the light
dis-
tribution. Thus, this embodiment can achieve downsizing of the light-emitting
device.
This arrangement can achieve a thinned backlight module (i.e., light-emitting
module) with which non-uniform luminance is reduced, as will be mentioned
later.
Fig. 5 shows the light distribution characteristics obtained by using the
secondary lens
as a comparative example. Even without using any secondary lens, the light-
emitting
device in this embodiment can achieve substantially the same light
distribution charac-
teristics as when using a secondary lens.
[0017] Nine light-emitting devices with different heights (H) in the
optical axis direction of
the encapsulants 108 and different diameters (widths: W) of the encapsulants
in the top
view were fabricated. The results of their light distribution characteristics
are shown in
Figs. 6A-6I. The light-emitting element used therein was a blue LED having a
sub-
stantially square shape with one side of 600 [im in length in the planar view
and a
thickness of 150 [im. The light reflective film 106 formed on the main surface
of the
light-emitting element 105 is configured of eleven layers by repeatedly
forming a Sift
layer (82 nm in thickness) and a Zr02 layer (54 nm in thickness).
Regarding each of the nine light-emitting devices No. 1 to No. 9, the ratio of
the
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height (H) of the encapsulant to the diameter (width: W) of the encapsulant is
shown in
Table 1.
[Table 1]
No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 No.9
H(mm) 0.70 10.89 0.92 0.79 0.93 1.09 0.74 1.00 1.18
W(mm) 2.76 2.78 2.56 3.06 3.14 3.11 3.40 3.28 3.29
H/W 0.25 10.32 0.36 0.26 0.30 0.35 0.22 0.30 0.36
Result Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig.
6A 6B 6C 6D 6E 6F 6G 6H 61
As can be seen from the experimental results, the light distribution
characteristics did
not change so much due to the difference in the diameter of the encapsulant.
However,
the ratio of the height (H) of the encapsulant to the diameter (width: W) of
the en-
capsulant affected the light distribution characteristics.
The graphs of Figs. 6A-61 show that the ratio (H/W) of the height (H) to the
width (W)
of the encapsulant is preferably 0.3 or less in order to achieve a wider light
dis-
tribution.
[0018] Preferred examples of the light-emitting device 100 in this
embodiment will be
described below.
(Base 101)
The base 101 is a member for mounting the light-emitting element 105. The base
101
has the conductive wirings 102 on its surface to supply electric power to the
light-
emitting element 105.
Examples of a material for the base 101 can include ceramics, and resins such
as a
phenol resin, an epoxy resin, a polyimide resin, a BT resin, polyphthalamide
(PPA),
and polyethylene terephthalate (PET). Among them, the resin is preferably
selected as
the material in terms of low cost and formability. The thickness of the base
can be
selected as appropriate. The base may be either a rigid base or a flexible
base manu-
facturable by a roll-to-roll system. The rigid base may be a thinned rigid
base that is
bendable.
[0019] To obtain the light-emitting device with high resistance to heat and
light, ceramics
are preferably selected as the material for the base 101. Examples of ceramics
can
include alumina, mullite, forsterite, glass-ceramics, nitride-based (e.g., AN)
ceramics,
and carbide-based (e.g., SiC) ceramics. Among them, ceramics made of alumina
or
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mainly containing alumina are preferable.
[0020] In the use of a resin as the material for the base 101, an inorganic
filler such as glass
fiber, Si02, Ti02, or A1203, is mixed into the resin, thereby allowing the
base to have
improved mechanical strength and improved optical reflectance, reduced thermal
expansion rate, and the like. The base 101 may be any other member as long as
it can
separate and insulate a pair of conductive wirings 102 from each other. The
base 101
may employ a so-called metal base that includes a metal member with an
insulating
layer formed therein.
[0021] (Conductive Wiring 102)
The conductive wirings 102 are members electrically connected to electrodes of
the
light-emitting element 105 and adapted to supply current (electric power) from
the
outside to the light-emitting element. That is, the conductive wiring serves
as an
electrode or a part thereof for energization with the power from the outside.
Normally,
the conductive wirings are formed of at least two wirings, namely, positive
and
negative wirings spaced apart from each other.
[0022] Each conductive wiring 102 is formed over at least an upper surface
of the base that
serves as a mounting surface for the light-emitting element 105. Material for
the
conductive wiring 102 can be selected as appropriate, depending on material
used for
the base 101, a manufacturing method thereof, and the like. For example, when
ceramic is used as the material for the base 101, the conductive wirings 102
are
preferably made of material having a high melting point that can withstand the
sintering temperature of a ceramic sheet. Specifically, metal with a high
melting point,
such as tungsten or molybdenum, is preferably used as the material for the
conductive
wiring. Further, other metal materials, such as nickel, gold, or silver may be
formed to
cover the above-mentioned surface of the conductive wiring by plating,
sputtering,
vapor deposition, etc.
[0023] When the glass epoxy resin is used as the material for the base 101,
the material for
the conductive wiring 102 is preferably made of material that is easy to
process. In the
case of using the epoxy resin injection-molded, the conductive wiring 102 is
made of
material that can be easily processed by punching, etching, bending, etc., and
has a
relatively high mechanical strength. Specifically, examples of the conductive
wiring
can include metals, such as copper, aluminum, gold, silver, tungsten, iron,
and nickel,
and a metal layer or lead frame made of an iron-nickel alloy, phosphor bronze,
an iron-
copper alloy, molybdenum, and the like. The surface of the lead frame may be
coated
with a metal material other than that of a lead frame main body. Such metal
materials
can be appropriately selected, for example, silver alone, or an alloy of
silver and
copper, gold, aluminum or rhodium. Alternatively, the conductive wiring can be
formed of multiple layers using silver or each alloy. Suitable methods for
coating with
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a metal material can include sputtering, vapor deposition, and the like as
well as the
plating.
[0024] (Bonding member 103)
The bonding members 103 are members for fixing the light-emitting element 105
onto the base 101 or conductive wirings 102. In the flip-chip mounting,
conductive
members are used as the bonding members in the same manner as in this
embodiment.
Specifically, suitable materials for the bonding member can include an Au-
containing
alloy, an Ag-containing alloy, a Pd-containing alloy, an In-containing alloy,
a Pb-Pd
containing alloy, an Au-Ga containing alloy, an Au-Sn containing alloy, an Sn-
containing alloy, an Sn-Cu containing alloy, an Sn-Cu-Ag containing alloy, an
Au-Ge
containing alloy, an Au-Si containing alloy, an Al-containing alloy, a Cu-In
containing
alloy, and a mixture of metal and a flux.
[0025] Suitable forms of the bonding member 103 can include a liquid-type,
a paste-type,
and/or a solid-type (e.g., sheet-shaped, block-shaped, wire-shaped and/or
powder-
form). The form of the bonding member can be selected based on the composition
thereof, the shape of the base, and the like, as appropriate. These bonding
members
103 may be formed of a single member or a combination of several kinds of
members.
[0026] (Insulating Member 104)
The conductive wirings 102 are preferably covered with the insulating member
104
except for parts thereof electrically connected to the light-emitting element
105 and
other materials. That is, as shown in the respective figures, a resist for
insulating and
covering the conductive wirings 102 may be disposed over the base. The
insulating
member 104 can function as such a resist.
[0027] In the case of disposing the insulating member 104, a white-based
filler can be
contained in the insulating member. The white-based filler contained in the
insulating
member can reduce leakage and absorption of light, thereby enabling
improvement of
the light extraction efficiency of the light-emitting device 100 as well as
insulating the
conductive wirings 102.
Material for the insulating member 104 can be appropriately selected on the
basis
that the material is less likely to absorb the light from the light-emitting-
element and
have an insulating property. Examples of the material for the insulating
member can
include epoxy, silicone, modified silicone, urethane, oxetane, acrylic,
polycarbonate,
and polyimide resins.
[0028] (Light-Emitting Element 105)
The light-emitting element 105 mounted on the base can be one known in the
art. In
this embodiment, a light-emitting diode is preferably used as the light-
emitting element
105.
A light-emitting element 105 that emits light at an appropriate wavelength can
be
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selected. For example, a blue or green light-emitting element can utilize
ZnSe, a
nitride-based semiconductor (In,AlyGai , yN, 0 X, 0 Y, X + Y 1), or GaP. A
light
transmissive sapphire substrate and the like can be used as a growth
substrate. A red
light-emitting element can use GaAlAs, AlInGaP, etc. Moreover, semiconductor
light-
emitting elements made of any material other than the materials mentioned
above can
also be used. The composition, emission color, and size of the light-emitting
element
for use, and the number of light-emitting elements for use, and the like can
be selected
as appropriate in accordance with the purpose.
[0029] Various emission wavelengths can be selected depending on the
material of the semi-
conductor layer and a mixed crystal ratio thereof. The light-emitting element
may have
positive and negative electrodes on the same surface side to enable the flip-
chip
mounting, or may alternatively have positive and negative electrodes on its
different
surfaces.
[0030] The light-emitting element 105 in this embodiment has a light
transmissive substrate,
and a semiconductor layer stacked on the substrate. The semiconductor layer
includes
an n-type semiconductor layer, an active layer, and a p-type semiconductor
layer
formed in this order. An n-type electrode is formed on the n-type
semiconductor layer,
and a p-type electrode is formed on a p-type semiconductor layer.
[0031] As shown in Fig. 1, the light-emitting element 105 is mounted in a
flip-chip manner
on the conductive wirings 102 disposed on the surface of the base 101 via the
bonding
members 103. A surface of the light-emitting element 105 opposed to the
surface
thereof with the electrodes formed thereon, that is, a main surface of the
light
transmissive substrate would serve as a light extraction surface. However, in
this em-
bodiment, the light reflective film 106 is formed on the light extraction
surface, and
thus the lateral surface of the light-emitting element 105 practically serves
as the light
extraction surface. That is, part of the light emitted from the light-emitting
element 105
and directed toward the main surface of the light-emitting element 105 is
returned to
the light-emitting element 105 by the light reflective film 106, then
repeatedly
reflected inside the light-emitting element 105, and eventually output from
the lateral
surfaces of the light-emitting element 105. Therefore, the light distribution
charac-
teristics of the light-emitting device 100 (see the dotted line in Fig. 4)
exhibit the char-
acteristics of a combination of the light passing through the light reflective
film 106
and the light emitted from the lateral surfaces of the light-emitting element
105.
[0032] The light-emitting element 105 is disposed to straddle the region
between the two
conductive wirings 102 that are isolated and insulated on positive and
negative sides.
The light-emitting element 105 is electrically connected and mechanically
fixed to the
conductive wirings via the conductive bonding members 103. To mount the light-
emitting element 105, a method using bumps can be employed as well as a method
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using solder paste. As a light-emitting element 105, a small-sized package
product
which includes the light-emitting element encapsulated with a resin or the
like can also
be used. The shape or structure of the light-emitting element 15 can be
appropriately
selected.
[0033] As will be described below, in the case of the light-emitting device
including a
wavelength conversion member, the light-emitting element suitably uses a
nitride
semiconductor (In,AlyGai , yN, 0 X, 0 Y, X + Y 1) capable of emitting light
with
a short wavelength that can efficiently excite a wavelength conversion layer.
[0034] Although an embodiment using flip-chip mounting has been described
as an
example, certain embodiments of the present invention may employ a mounting
state
in which an insulating base side of a light-emitting element serves as the
mounting
surface, and electrodes formed on the upper surface of the light-emitting
element are
connected to wires. In this case, the upper surface of the light-emitting
element is an
electrode-formed surface side, and the light reflective film is positioned on
the
electrode-formed surface side.
[0035] (Light Reflective Film 106)
The light reflective film 106 is formed on the light extraction surface side,
which is
the main surface of the light-emitting element 105.
Material for the light reflective film may be one which reflects at least the
light
emitted from the light-emitting element 105, for example, metal or resin
containing a
white filler.
A dielectric multilayer film can be used to produce the reflective film with
less light
absorption. Additionally, the reflectance of the light reflective film can be
suitably
adjusted by designing the dielectric multilayer film, or its reflectance can
also be
controlled by adjusting the angle of the light. In particular, the reflectance
is increased
in the direction perpendicular to the light extraction surface (also called
the optical axis
direction), and decreased at a large angle relative to the optical axis due to
increase of
the light transmissivity of the reflective film, which can control the shape
of the
batwing light distribution.
[0036] Regarding a reflection wavelength range in the optical axis
direction of the dielectric
multilayer film, i.e. in the direction perpendicular to the upper surface of
the light-
emitting element, as shown in Fig. 3, it is preferable to widen a region on a
long
wavelength side of the reflection wavelength range, with respect to the
emission peak
wavelength of the light-emitting element 105.
This is because as the angle from the optical axis is varied, in other words,
as the
angle from the optical axis of the incident light is increased, the reflection
wavelength
range of the dielectric multilayer film is shifted to the short wavelength
side. By
widening the reflection wavelength range toward the long wavelength side with
respect
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to the emission wavelength, the adequate reflectance can be maintained up to a
wide
angle, that is, for light incident from the light-emitting element at a large
angle relative
to the optical axis.
Materials suitable for use in the dielectric multilayer film can be a metal
oxide film
material, a metal nitride film, an oxynitride film, or the like. Organic
materials, such as
a silicone resin or a fluorine resin, can also be used. However, the material
for the di-
electric multilayer can be selected from ones other than those described
above.
[0037] (Encapsulant 108)
Materials suitable for use in the encapsulant 108 can be light transmissive
materials,
including an epoxy resin, a silicone resin, a mixed resin thereof, or glass.
Among them,
the silicone resin is preferably selected by taking into consideration the
resistance to
light and the formability.
[0038] The encapsulant 108 can contain: a light diffusion material, a
wavelength conversion
material, such as phosphors or quantum dots that absorbs part of light from
the light-
emitting element 105 to output light with a different wavelength from that of
the light
emitted from the light-emitting element; and a colorant corresponding to the
color of
emitted light from the light-emitting element.
In the case of adding these materials to the encapsulant 108, it is preferable
to use
ones less likely to affect the light distribution characteristics. For
example, the material
having a particle size of 0.2 [im or less is preferable because it less likely
to affects the
light distribution characteristics. The term "particle size" as used in the
present speci-
fication means an average particle size, and the average particle size is
measured based
on a Fisher-SubSieve-Sizers-No. (F.S.S.S.No) using an air permeability method.
[0039] The encapsulant 108 can be formed by compression molding or
injection molding to
cover the light-emitting element 105. Alternatively, the material for the
encapsulant
108 is optimized its viscosity to be dropped or drawn on the light-emitting
element
105, thereby controlling the shape of the encapsulant 108 by the surface
tension of the
material itself.
[0040] In the latter formation method, a mold is not required, so that the
encapsulant can be
formed by a simpler method. Other than adjusting the viscosity of the base
material of
the encapsulant 108, the viscosity of the encapsulant material can be adjusted
by using
the above-mentioned light diffusion material, wavelength conversion material,
and/or
colorant to form the encapsulant 108 with a desired level of viscosity.
[0041] Second Embodiment
Fig. 7 is a cross-sectional view of a light-emitting module 300 including a
light-
emitting device 200 in a second embodiment. In this embodiment, a plurality of
the
light-emitting elements 105 is mounted at predetermined intervals on the base
101. At
least one light reflective member 110 is disposed between the adjacent light-
emitting
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elements 105 so as to reflect the light emitted at a small angle relative to
the upper
surface of the light-emitting element (i.e., upper surface of the base 101).
That is, the
light-emitting device 200 is an integrated light-emitting device that includes
a plurality
of the light-emitting devices 100 of the first embodiment and the light
reflective
member 110 disposed between the respective light-emitting devices 100. A light
diffusion plate 111 for diffusing the light from the light-emitting element
105 is
disposed above the light-emitting devices 100 and the light reflective member
110 and
substantially in parallel with the upper surfaces of the light-emitting
elements. A
wavelength conversion layer 112 for converting part of the light emitted from
the light-
emitting elements 105 to light with a different wavelength is disposed above
the light
diffusion plate 111 and substantially in parallel with the light diffusion
plate 111.
[0042] In general, as the ratio of a distance between the base 101 and the
light diffusion
plate 111 (hereinafter may be referred to as an optical distance: OD) to a
distance
between the adjacent light-emitting elements (hereinafter may be referred to
as a pitch)
is decreased, the amount of light between the light-emitting elements 105 on
the
surface of the light diffusion plate 111 becomes small, causing a dark space.
However, with the arrangement including the light reflective member 110
disposed
in this way, the light reflected by the light reflective member 110
compensates for the
amount of light between the light-emitting elements, whereby the non-uniform
luminance on the surface of the light diffusion plate 111 can be reduced even
in a
region with a smaller ratio of OD/Pitch.
Specifically, in the light-emitting device 200 of the second embodiment, an in-
clination angle 0 of a light reflective surface of the light reflective member
110 relative
to the base 101 is set such that the non-uniform luminance on the surface of
the light
diffusion plate 111 is reduced taking into consideration the light
distribution charac-
teristics of the respective light-emitting devices 100. Regarding the light
distribution
characteristics of the plurality of light-emitting devices 100 arranged, each
light-
emitting device 100 preferably has the light distribution characteristics that
the amount
of light becomes large in a region with a large light distribution angle,
i.e., in a region
at a light distribution angle of around 90 , in order to reduce the non-
uniform
luminance on the surface of the light diffusion plate 111 and to achieve the
thinned
light-emitting device 200.
[0043] When the ratio of OD/Pitch is small, for example, 0.2 or less, an
elevation angle at
which the incident light enters the light reflective member 110 is less than
22 relative
to the light-emitting surface of the light-emitting element 105. Thus, to
increase the re-
flectance of the light by the light reflective member 110 at the low OD/Pitch
of 0.2 or
less, the light distribution characteristics of the light-emitting device 100
preferably has
the feature that, for example, the amount of light at the elevation angle of
less than 20
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relative to the upper surface of the base is large. Specifically, the first
and second
peaks of the emission intensity are preferably positioned in a range of the
elevation
angle of less than 200. Here, the elevation angle of 20 corresponds to the
light dis-
tribution angles of 20 and 160 in Fig. 4. In other words, the first peak of
emission
intensity is positioned in a range of less than 20 of the light distribution
angle, and the
second peak of emission intensity is positioned in a range of greater than 160
of the
light distribution angle, as shown in Fig. 4. The amount of light in a range
of the
elevation angle of less than 20 is preferably 30% or more of the whole amount
of
light, and more preferably 40% or more thereof.
[0044] (Light Reflective Member 110)
The light reflective member 110 is provided between the adjacent light-
emitting
elements 105.
The light reflective member may be formed of a material that reflects at least
light
with the emission wavelength of the light-emitting element 105. For example, a
metal
plate or resin containing a white filler can be suitably used for the light
reflective
member.
A dielectric multilayer film can be used as a reflective surface of the light
reflective
member to produce the reflective surface with less light absorption.
Additionally, the
reflectance of the light reflective member can be appropriately adjusted by
designing
the dielectric multilayer film, or its reflectance can also be controlled by
the angle of
the light.
[0045] The height of the light reflective member 110 and the inclination
angle 0 of the light
reflective surface relative to the surface of the base 101 can be set to
appropriate
values. The reflective surface of the light reflective member 110 may be a
planar
surface or a curved surface. To obtain the desired light distribution
characteristics, the
suitable inclination angle 0 and shape of the reflective surface can be set.
The height of
the light reflective member 110 is preferably set at 0.3 times or less and
more
preferably 0.2 times or less the distance between the adjacent light-emitting
elements.
This arrangement can provide the thinned light-emitting module 300 with less
non-
uniform luminance.
[0046] For the light-emitting device 200 used in an environment where the
use temperature
tends to change significantly, the linear expansion coefficient of the light
reflective
member 110 needs to be close to that of the base 101. In the case where the
light re-
flective member 110 significantly differs from the base 101 in the linear
expansion co-
efficient, warpage might occur in the light-emitting device 200 due to the
change in
temperature, or otherwise the positional relationship between the components,
es-
pecially, between the light-emitting device 100 and the light reflective
member 110
might shift, thus possibly failing to obtain the desired optical properties.
However, the
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linear expansion coefficient is a physical property and thus there are not so
many al-
ternatives in reality. For this reason, the light reflective member 110 is
preferably
formed by a film molded component that is elastically deformable in order to
reducing
the occurrence of warpage of the light-emitting device 200 even in the case
where the
light reflective member significantly differs from the base in the linear
expansion co-
efficient. This is because the light reflective member 110 made of a less
elastically de-
formable material, such as solid material tends to expand while maintaining
its shape,
but the film-shaped light reflective member can be appropriately deformed to
compensate its expansion.
[0047] Preferably, a plurality of the light reflective members 110 is
coupled together into a
plate shape to have through holes 113 where the light-emitting devices 200 are
disposed. Fig. 8 shows such a plate-shaped light reflective plate 110'. Fig.
8A is a top
view of the light reflective plate 110', and FIGT. 8B is a cross-sectional
view taken
along the line A-A of Fig. 8A. Such a light reflective plate 110' can be
formed by
metal molding, vacuum forming, pressure molding, press forming, and the like.
The
light reflective plate 110' is disposed on the base 101. The light reflective
member 110
may be formed by a method which involves drawing a light reflective resin
directly on
the base 101, and the like. The height of the light reflective member 110 is
preferably
set at 0.3 times or less the distance between the adjacent light-emitting
elements, and
for example, more preferably 0.2 times or less the distance between the
adjacent light-
emitting elements.
[0048] Example 1
In this example, as shown in Fig. 1, a glass-epoxy-based material is used for
the base
101, and a Cu material of 35 [im in thickness is used as the conductive
wiring.
A nitride-based blue LED may be used as the light-emitting element 105. The
LED
has an approximately square shape with one side of 600 [im in length in the
planar
view and a thickness of 150 [im. An epoxy-based white solder resist may be
used as
the insulating member 104.
The light reflective film 106 formed on the main surface of the light-emitting
element
105 is configured of eleven layers by repeatedly forming a 5i02 layer (82 nm
in
thickness) and a Zr02 layer (54 nm in thickness).
At this time, the light transmissivity of the light reflective film 106 is
shown in Fig.
2. The light transmissivity in the direction perpendicular to the main surface
side of the
light-emitting element (i.e., in the optical axis direction) is low, and the
light trans-
missivity of the light reflective film is increased as an angle away from the
optical axis
increases.
The light-emitting element 105 is covered with the encapsulant 108. The
encapsulant
108 is formed of a silicone resin and has a height (H) of 1.0 mm and a
diameter of the
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bottom surface (W) of 3.0 mm.
With this arrangement, the light emitted from the light-emitting element 105
is
refracted at an interface between the encapsulant 108 and air, which widens
the range
of the light distribution angles. The light distribution characteristic of the
light-emitting
device 100 obtained by this arrangement is indicated by the solid line in Fig.
4. The
light distribution characteristic obtained by a light-emitting device without
the en-
capsulant 108 is indicated by the dotted line in Fig. 4. In this way, the
encapsulant 108
is used together with the light reflective film 106, which can achieve the
lower OD/
Pitch.
[0049] Example 2
In Example 2, a plurality of light-emitting elements 105 of Example 1 are
mounted
on the base 101, and the at least one light reflective member 110 is disposed
between
the adjacent light-emitting elements. Here, Pitch is set at 12.5 mm.
The light reflective member 110 is a plate-shaped light reflective plate,
which is
formed using a polypropylene sheet containing a TiO2 filler (having a
thickness (t) of
0.2 mm) by the vacuum forming method so as to have a reflection angle 0 (i.e.,
elevation angle) of 550 and a height of 2.4 mm. The light reflective member
110 is a
plate-shaped light reflective plate shown in Fig. 8 and disposed on the
insulating
member 104.
Over the light reflective member 110, a milky-white light diffusion plate 111
and a
wavelength conversion layer 112 are disposed to form a liquid crystal
backlight (i.e.,
light-emitting module). In this arrangement, Figs. 9A and 9B show the result
of
comparison of the non-uniform luminance on the surface of the light diffusion
plate
111 between the presence and absence of the light reflective member 110. Fig.
9A
shows a light-emitting module without light reflective member, and Fig. 9B
shows a
light-emitting module in the presence of the light reflective member. As shown
in Figs.
9A and 9B, in the case where the light reflective member is not disposed, the
relative
luminance is decreased to in a range of about 0.6 to about 0.7 within a region
where
the relative luminance tended to be high (i.e., in a range of the number of
pixels
between about 250 pixels to about 720 pixels). On the other hand, in the case
where the
light reflective member is disposed, the relative luminance is not decreased
to below
about 0.8 within the region where the relatively luminance tended to be high
(i.e., at
the number of pixels between about 250 pixels to about 720 pixels). In other
words, it
can be seen the effect that non-uniform luminance is improved by providing the
light
reflective member.
[0050] The light-emitting device and light-emitting module of the present
embodiments can
be used in backlight light sources for liquid crystal displays, various
lighting fixtures,
and the like.
