U.S. patent application number 15/802703 was filed with the patent office on 2018-03-15 for light-emitting device with improved flexural resistance and electrical connection between layers, production method therefor, and device using light-emitting device.
This patent application is currently assigned to TOSHIBA HOKUTO ELECTRONICS CORPORATION. The applicant listed for this patent is TOSHIBA HOKUTO ELECTRONICS CORPORATION. Invention is credited to Keiichi MAKI.
Application Number | 20180076364 15/802703 |
Document ID | / |
Family ID | 51624417 |
Filed Date | 2018-03-15 |
United States Patent
Application |
20180076364 |
Kind Code |
A1 |
MAKI; Keiichi |
March 15, 2018 |
LIGHT-EMITTING DEVICE WITH IMPROVED FLEXURAL RESISTANCE AND
ELECTRICAL CONNECTION BETWEEN LAYERS, PRODUCTION METHOD THEREFOR,
AND DEVICE USING LIGHT-EMITTING DEVICE
Abstract
A light-emitting device includes a pair of light-transmissive
insulator sheets disposed opposite to each other and two types of
light-transmissive electroconductive layers disposed on a common
one of or separately on one and the other of the pair of
light-transmissive insulator sheets, and at least one
light-emitting semiconductor each provided with a cathode and an
anode which are individually and electrically connected to the two
types of the light-transmissive electroconductive layers. The
electrical connection and mechanical bonding between the members
are improved by a light-transmissive elastomer which is between the
pair of light-transmissive insulator sheets. A method in which a
light-emitting semiconductor element and a light-transmissive
electroconductive member are subjected to vacuum hot-pressing.
Inventors: |
MAKI; Keiichi; (Asahikawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOSHIBA HOKUTO ELECTRONICS CORPORATION |
Asahikawa |
|
JP |
|
|
Assignee: |
TOSHIBA HOKUTO ELECTRONICS
CORPORATION
Asahikawa
JP
|
Family ID: |
51624417 |
Appl. No.: |
15/802703 |
Filed: |
November 3, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14771816 |
Sep 1, 2015 |
9837587 |
|
|
PCT/JP2014/058747 |
Mar 27, 2014 |
|
|
|
15802703 |
|
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|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/56 20130101;
H01L 33/38 20130101; H01L 33/62 20130101; H01L 25/0753 20130101;
H01L 33/387 20130101; H01L 2933/005 20130101; H01L 33/54 20130101;
H01L 2924/07811 20130101; H01L 2224/16225 20130101; B32B 17/10036
20130101; H01L 2924/07811 20130101; H01L 2924/00 20130101; H01L
2924/00014 20130101; H01L 2924/12041 20130101 |
International
Class: |
H01L 33/54 20100101
H01L033/54; H01L 33/56 20100101 H01L033/56; H01L 33/38 20100101
H01L033/38; H01L 33/62 20100101 H01L033/62 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2013 |
JP |
2013-069988 |
Mar 28, 2013 |
JP |
2013-069989 |
Claims
1. A flexible light-emitting device, comprising: a pair of
light-transmissive insulator sheets each provided with a
light-transmissive electroconductive layer, or a pair of a
light-transmissive insulator sheet provided with light-transmissive
electroconductive layers and a light-transmissive insulator sheet
which is free from a light-transmissive electroconductive layer,
disposed opposite to each other so as to form a region between the
pair, one or more light-emitting semiconductor element each
provided with a cathode and an anode which are individually and
electrically connected to respective ones of said
light-transmissive electroconductive layers, and a
light-transmissive elastomer, respectively disposed between the
pair of light-transmissive insulator sheets so as to fill the
region in combination, wherein the light-transmissive elastomer is
at least partially present in the interface between the cathode and
anode of the light-emitting semiconductor element and the
light-transmissive electroconductive layers, the light-transmissive
elastomer is also filled in concavities of the cathode and anode
surfaces, and the light-emitting device exhibits a flexural
resistance in terms of a lighting maintenance rate of at least 3/6
at a bending radius of 20 nm or at least 5/6 at a bending radius of
30 mm when the light-emitting device in a lighting state is wound
about a round bar having a specified bending radius.
2. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer covers 10-90% each of the cathode area
and the anode area of said light-emitting semiconductor
element.
3. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer has a Vicat softening temperature of
80-160.degree. C.
4. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer has a melting temperature which is at
least 180.degree. C. or at least 40.degree. C. higher than Vicat
softening temperature.
5. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer has a tensile storage elastic modulus
of 0.01 GPa-10 GPa in a temperature range of 0 to 100.degree.
C.
6. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer has a glass transition temperature of
at most -20.degree. C.
7. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer is not melted at the Vicat softening
temperature, or has a tensile storage elastic modulus of at least
0.1 MPa at the Vicat softening temperature.
8. The light-emitting device according to claim 1, wherein each of
the cathode and anode of the light-emitting semiconductor element
has a surface roughness Ra of 0.1-10 .mu.m.
9. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer comprises an acrylic elastomer.
10. The light-emitting device according to claim 1, wherein said
light-transmissive elastomer is a polymeric elastic material.
11. The light-emitting device according to claim 1, wherein the
light-transmissive electroconductive layer comprises a conductor
film, a transparent resin layer containing a particulate conductor,
or a mesh electrode.
12. The light-emitting device according to claim 1, wherein the
light-transmissive electroconductive layer comprises a sputtered
film or vapor-deposited film of a conductor.
13. The light-emitting device according to claim 1, wherein the
light-transmissive electroconductive layer comprises a mesh
electrode layer.
14. The light-emitting device according to claim 1, wherein the
light-transmissive electroconductive layer comprises a plurality of
light-transmissive electroconductive fillers and a
light-transmissive resin binder binding the electroconductive
fillers in a mutually contacting state.
15. The light-emitting device according to claim 14, wherein the
electroconductive fillers occupy 50-95 wt. % of the
light-transmissive electroconductive layer.
16. The light-emitting device according to claim 1, wherein at
least one of the anode and the cathode of the light-emitting
semiconductor element is connected to a corresponding
light-transmissive electroconductive layer via a bump
electrode.
17. The light-emitting device according to claim 1, wherein the
light-transmissive electroconductive layer has a sheet resistivity
of at most 1000 ohm/.quadrature..
18. The light-emitting device according to claim 1, wherein the
light transmissive electroconductive layer has a thickness of
0.1-10 .mu.m.
19. The light-emitting device according to claim 1, which is free
from bubbles having an outer diameter which is equal to or larger
than 500 .mu.m or the chip size of the light-emitting semiconductor
element.
20. A process for producing a light-emitting device according to
claim 1, comprising: disposing a light-transmissive elastomer
between an electrode surface of a light-emitting semiconductor
element and a surface of a light-transmissive electroconductive
layer of a light-transmissive electroconductive member, and then
subjecting the light-emitting semiconductor element and the
light-transmissive electroconductive member to vacuum hot pressing
at a temperature which is in a range of from 10.degree. C. below to
30.degree. C. above the Vicat softening temperature of the
light-transmissive elastomer.
21. An apparatus, comprising a display apparatus or an illumination
apparatus including a light-emitting device according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/771,816, filed Sep. 1, 2015, which in turn is the National
Stage of International Application No. PCT/JP2014/058747, filed
Mar. 27, 2014, which is based on and claims the priorities of
Japanese Application No. 2013-069988, filed Mar. 28, 2013, and
Japanese Application No. 2013-069989, filed Mar. 28, 2013, of each
of which the benefits are claimed herein and the entire disclosures
of each are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The embodiments relate to a light-transmissive
light-emitting device equipped with light-emitting elements, its
production method, and an apparatus using the light-emitting
device.
BACKGROUND OF THE INVENTION
[0003] A light-transmissive light-emitting device is formed by
electrically connecting electrodes disposed on light-emitting
elements to light-transmissive electroconductive layers on a
substrate. As the connection method, the wirebonding method has
been used conventionally but is not desirable as a connection
method for use in a device requiring translucency, such as a touch
panel or a light-emitting device.
[0004] On the other hand, Patent documents 1-5 disclose methods not
using the wirebonding method for connecting light-emitting elements
in a light-emitting device.
[0005] Light-transmissive light-emitting devices disclosed in
Patent documents 3-5 are useful for achieving a curved shape which
cannot be realized by conventional nonflexible light-transmissive
light-emitting devices.
PRIOR ART DOCUMENTS
Patent Documents
[0006] Patent document 1: JP-A 11-177147
[0007] Patent document 2: JP-A 2002-246418
[0008] Patent document 3: JP-A 2007-531321
[0009] Patent document 4: JP-A 2009-512977
[0010] Patent document 5: JP-A 2012-84855.
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0011] However, as for a flexible light-transmissive light-emitting
device used at windows or exterior of, e.g. a car, a train, a
vessel, an airplane, etc., such a light-transmissive light-emitting
device is required to satisfy reliabilities under a wide
temperature range and under application of repetitive stresses.
Unless reliabilities are satisfied so as to clear the
above-mentioned repetitive environmental conditions and operating
conditions, the use of a flexible light-transmissive light-emitting
device will be restricted extremely. From such viewpoints, the
light-emitting devices disclosed in Patent documents 3, 4, and 5
lack sufficient reliabilities and the practical utilities thereof
were limited.
[0012] Moreover, the light-emitting devices disclosed in Patent
documents 3, 4 and 5 are accompanied with problems that, under
application of a pressure during the production thereof, electrode
edges formed on the light-emitting device, the concavities and
convexities formed on the electrodes, a level difference at edges
of an active layer and the device substrate, etc., are abutted
against the light-transmissive conductive layer of a
light-transmissive electroconductive member, thus being liable to
result in a crack in or breakage of the light-transmissive
conductive layer and cause disconnection leading to a lowering in
production yield and an increase in production cost. Furthermore,
since the light-emitting devices disclosed in Patent documents 3, 4
and 5 are accompanied with fine cracks in the light-transmissive
conductive layer of light-transmissive electroconductive member
during the production thereof in many cases, thus being liable to
cause lighting failure in case of being bent or under application
of a heat cycle, even if they are lighting immediately after
production.
[0013] Furthermore, since the light-emitting devices disclosed in
Patent documents 4 and 5 are insufficient in contact between the
light-transmissive conductive layer and the LED electrodes, they
have poor resistance to bending and leave a problem in reliability
after application of heat or thermal cycles.
[0014] An embodiment of the present invention has been developed in
view of the above-mentioned situation, and an object thereof is to
provide a light-emitting device which is excellent in flexural
resistance or in heat cycle characteristic during production or in
use, or capable of persistent lighting in resistance to flexure or
application of heat load, a process for production thereof and an
apparatus using the light-emitting device.
Means for Solving the Problems
[0015] The inventor tested light-emitting devices including a
light-transmissive elastomer disposed between a light-emitting
diode (LED) chip as an example of a light-emitting element and a
light-transmissive electroconductive layer, and has discovered
influences of a ratio of an area of presence of the
light-transmissive elastomer to an area of the electrode of the LED
chip, and a proportion of the light-transmissive elastomer present
at concavities of unevenness of the electrode layer on the flexural
resistance of the light-emitting device. The inventor has also
discovered influences of the ratio of the area of presence of the
light-transmissive elastomer between the LED chip and the
light-transmissive electroconductive layer to the electrode area of
the LED chip, and the proportion of the light-transmissive
elastomer present at concavities of unevenness of the electrode
layer on the heat-cycle resistance of the light-emitting device.
The term "flexural resistance" used herein refers to a resistance
to deteriorations, such as crack, breakage and disconnection, when
a film or sheet-like product or material subjected to a flexure
(bending) or a repetition of flexures at a certain curvature
radius.
[0016] A light-emitting device of this embodiment has been
developed to solve the above-mentioned problem, and comprises:
[0017] a pair of light-transmissive insulator sheets each equipped
with a light-transmissive electroconductive layer, or a pair of a
light-transmissive insulator sheet equipped with light-transmissive
electroconductive layers and a light-transmissive insulator sheet
free from a light-transmissive electroconductive layer, disposed
opposite to each other so as to form a region between the pair,
[0018] at least one light-emitting semiconductor element each
provided with a cathode and an anode which are individually
electrically connected to one and the other of said
light-transmissive electroconductive layers, and a
light-transmissive elastomer, respectively disposed between the
pair of light-transmissive insulator sheets so as to fill the
region in combination,
[0019] wherein the light-transmissive elastomer is at least
partially present in the interface between the cathode and anode,
respectively, of the light-emitting semiconductor element and the
light-transmissive electroconductive layers, and
[0020] the light-transmissive elastomer is also filled in
concavities of the cathode and anode surfaces. Herein, the
"light-emitting semiconductor element" refers generically to an
element wherein a luminescence layer comprising a semiconductor
causes luminescence under application of an electric field
(current) formed between a pair of electrode electrically connected
with the luminescence layer, which may be represented by a
light-emitting diode (LED), but not restricted thereto and can also
include an organic EL device and a laser diode.
[0021] A process for producing a light-emitting device according to
an embodiment has been developed to solve the above-mentioned
problem, and comprises:
[0022] disposing a light-transmissive elastomer between an
electrode surface of a light-emitting semiconductor element and a
surface of a light-transmissive electroconductive layer of a
light-transmissive electroconductive member, and
[0023] then subjecting the light-emitting semiconductor element and
the light-transmissive electroconductive member to vacuum hot
pressing at a temperature which is in a range of from 10.degree. C.
below the Vicat softening temperature to 30.degree. C. or
20.degree. C. above the Vicat softening temperature, respectively,
of the light-transmissive elastomer.
[0024] An apparatus according an embodiment has been developed to
solve the above-mentioned problem, is characterized by including
the above-mentioned light-emitting device, and may representatively
provide a display apparatus or an illumination apparatus.
Effect of the Invention
[0025] According to an embodiment of the present invention, there
are provided: a light-emitting device that includes a
light-transmissive electroconductive member comprising a
light-transmissive electroconductive layer held on a
light-transmissive insulator sheet, of which the light-transmissive
electroconductive layer can hardly cause a crack or a fracture,
that is excellent in flexural resistance or heat-cycle
characteristic and that can hardly cause bubbles remaining therein,
a process for production of the light-emitting device; and an
apparatus including the luminescent device.
[0026] More specifically, the light-emitting device (or an
apparatus including it) is characterized in that the sandwiching of
a light-transmissive elastomer between an LED chip and a
light-transmissive electroconductive layer, followed by hot
pressing under vacuum, is effective for improving the adhesion
between the light-transmissive elastomer and the transparent
electroconductive member and preventing the occurrence of crack or
breakage in the light-transmissive electroconductive layer, and
also for partial intrusion of the elastomer between the electrode
surface of the LED and the light-transmissive electroconductive
layer to enhance the mechanical junction by the elastomer
therebetween. As a result, even when the light-emitting device is
subjected to severe bending or application of a heat cycle, the
light-transmissive electroconductive layer does not readily cause a
crack or a breakage, and a reliable electrical connection between
the light-transmissive electro-conductive layer and the LED chip
electrode is ensured, to allow a persistent lighting under such
severe conditions.
[0027] Moreover, as the elastomer is processed under vacuum while
preventing the melt-fusion of the elastomer causing a low-viscosity
state, the remaining of air bubbles in the resultant light-emitting
device is prevented. If the hot pressing is performed under an
atmospheric pressure or a slight degree of reduced pressure, air
bubbles remain especially in the circumference of the LED chip
within the resultant light-emitting device and the air bubbles
compressed during the hot pressing are liable to swell after the
hot pressing, thus being further liable to cause a peeling between
the LED chip electrode and the light-transmissive electroconductive
layer. Furthermore, if the elastomer inserted between the LED tip
and the light-transmissive electroconductive layer is melted or in
a low-viscosity state at the time of the hot pressing, the LED chip
is liable to be displaced or inclined to cause an electrical
connection failure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a sectional view of a light-emitting device of a
first embodiment.
[0029] FIG. 2 is a partial enlarged view of FIG. 1.
[0030] FIG. 3 is a partial enlarged view of a part A1 in FIG.
2.
[0031] FIG. 4 is an example of cross-sectional scanning electron
microscope photograph of the light-emitting device of the first
embodiment.
[0032] FIG. 5 is an example of scanning electron microscope
photograph showing a surface state of a first electrode layer 15A
of LED chip 10 after peeling between the first electrode layer 15A
and a first light-transmissive electroconductive member 20A.
[0033] FIGS. 6A to 6C show surface states of a first electrode
layer 15A of LED chip 10 after peeling between the first electrode
layer 15A and a first light-transmissive electroconductive member
20A in a light-emitting device of Example 3 according to the first
embodiment; among which FIG. 6A is a scanning electron microscope
photograph, FIG. 6B is an elemental mapping photograph for carbon
according to energy dispersion-type X-ray analysis (EDX), and FIG.
6C is an elemental mapping photograph for tin according to EDX.
[0034] FIG. 7 illustrates a production process for a light-emitting
device of a first embodiment.
[0035] FIG. 8 illustrates Production Example 1 for a light-emitting
device.
[0036] FIG. 9 illustrates Production Example 2 for a light-emitting
device.
[0037] FIG. 10 is a partial enlarged sectional view of a
light-emitting device 90 prepared by Production Example 1.
[0038] FIG. 11 is a partial enlarged view of a part B1 in FIG.
10.
[0039] FIG. 12 is a cross-sectional photograph of a light-emitting
device 90 prepared by Production Example 1.
[0040] FIG. 13 is a cross-sectional photograph of a light-emitting
device 90A prepared by Production Example 2.
[0041] FIG. 14 is a sectional view of a light-emitting device of a
second embodiment.
[0042] FIG. 15 is a sectional view of an LED chip for a
light-emitting device of the second embodiment.
[0043] FIG. 16 illustrates a production process for a
light-emitting device of the second embodiment.
[0044] FIG. 17 is a schematic cross section of an example of a
one-face electrode-type light-emitting device containing a bump
electrode.
[0045] FIG. 18 is a schematic cross section of an example of a
two-face electrode-type light-emitting device containing a bump
electrode.
[0046] FIG. 19 is a side view showing an example shape of Au bump
formed on a pad electrode.
[0047] FIG. 20 is a plan view showing an example of disposition of
bump electrodes in a one-face electrode-type light-emitting
device.
DETAILED DESCRIPTION OF THE INVENTION
[0048] In a light-emitting device according to an embodiment, a
light-transmissive elastomer is disposed between an electrode
surface of the LED chip and a light-transmissive electroconductive
layer of a light-transmissive electroconductive member, the
light-transmissive elastomer intrudes into gaps between concavities
of unevenness on the LED chip electrode and the light-transmissive
electroconductive layer, and the electrode layer of the LED chip
and the light-transmissive electroconductive layer are electrically
connected.
[0049] Incidentally, the sizes, such as thickness, width and
distance, described herein are all based on values measured after
standing for at least 1 hour in a room at a temperature of
20.degree. C..+-.2.degree. C. by means of a non-contact method,
e.g. optically, or by comparison with a calibrated standard length
after measurement through an electron microscope or an optical
microscope.
[0050] The light-emitting device of an embodiment, as a result of
the formation of a light-transmissive elastomer layer of a
relatively high storage modulus at gaps between the LED chip
electrode surface and the light-transmissive electroconductive
layer surface, is provided with little liability of causing a crack
and a fracture in the light-transmissive electroconductive layer
even when subjected to a severe bending or application of a heat
cycle to retain a sufficient contact between the light-transmissive
electroconductive layer and the LED chip electrode layer, thus
ensuring a reliable electrical connection therebetween and
persistent lighting.
[0051] Luminescent devices of embodiments are described in more
detail with reference to drawings. A light-emitting device of a
first embodiment is described first.
Luminescent Device
First Embodiment
[0052] FIG. 1 is a sectional view of an essential part of a
light-emitting device according to a first embodiment.
[0053] A light-emitting device 1, includes: an LED chip 10
including an LED body 11 and first and second electrode layers 15
(15A, 15B) formed on a front and a back face, respectively, of the
LED body 11; first and second light-transmissive electroconductive
members 20 (20A, 20B) respectively covering the LED chip 10 and
including transparent substrates 21 (21A, 21B) and first and second
light-transmissive electroconductive layers 25 (25A, 25B); and a
light-transmissive elastomer layer 30 joined to a circumference 13
of the LED chip 10 and also to the light-transmissive
electroconductive layer 25A of the light-transmissive
electroconductive member 20A and the light-transmissive
electroconductive layer 25B of the light-transmissive
electroconductive member 20B.
[0054] In short, the light-emitting device 1 is formed by
sandwiching the LED chip 10 with two sheets of the
light-transmissive electroconductive members 20A and 20B and
joining the LED chip 10 and the light-transmissive
electroconductive members 20A and 20B with the light-transmissive
elastomer layer 30.
<LED Chip>
[0055] FIG. 2 is a partial enlarged view of FIG. 1. FIG. 3 is a
partial enlarged view of a part A1 in FIG. 2. FIG. 4 is an example
of cross-sectional scanning electron microscope photograph of the
light-emitting device of the first embodiment. In FIG. 4, a
reference numeral 95 refers to a resin for fixing the
light-emitting device 1 as an objective sample for cross-sectional
observation thereof and is not a component of the light-emitting
device 1.
[0056] The LED chip 10 has a structure including an LED body 11
having a (laminate) layer structure corresponding to a
semiconductor luminescence layer of an LED, and an electrode layer
15A as a first electrode layer and a second electrode layer 15B as
a second electrode layer formed on both faces of the LED body
11.
[0057] Referring to FIG. 2, the LED body 11 has an N-type
semiconductor layer 42 and a P-type semiconductor layer 44 on a
semiconductor substrate 41 comprising GaAs, Si, GaP, etc., and also
a luminescence layer 43 formed between the N-type semiconductor
layer 42 and the P-type semiconductor layer 44.
[0058] The surface of the semiconductor substrate 41 and the
surface of the P-type semiconductor layer 44 constitute surfaces 71
of the LED body 11, respectively. Here, the surface of the
semiconductor substrate 41 is called a first face 71A of the LED
body 11 among the surfaces 71 of the LED body 11, and the surface
of P-type semiconductor layer 44 is called a second face 71B of the
LED body 11. The second face 71B is on the light-emitting side 85
of the LED chip 10. It is possible to form a transparent electrode
layer on the surface of P-type semiconductor layer 44. In this
case, this transparent electrode layer provides a second face
71B.
[0059] The electrode layer 15A is formed on the first face 71A of
the LED body 11, i.e., the surface of the semiconductor substrate
41, and forms a substrate-side electrode layer which is
electrically connected with N-type semiconductor layer 42 via the
semiconductor substrate 41. The electrode layer 15B is formed on
the second face 71B of the LED body 11, i.e., the surface of P-type
semiconductor layer 44, and forms a light-emitting-side electrode
layer electrically connected with the P-type semiconductor layer
44. The electrode layer 15B as the light-emitting side electrode
layer is formed on a side closer to the luminescence layer 43 than
the electrode layer 15A. In addition, it is possible to dispose a
reflective film on the semiconductor substrate 41 surface.
[0060] The electrode layer 15A (cathode in this example), as a
substrate-side electrode layer, may comprise, e.g. Au, and the
thickness is usually 0.1-2 .mu.m, preferably 0.3-1 .mu.m. The
electrode layer 15B (anode in this example) as a
light-emitting-side electrode layer, may comprise, e.g. Au, and the
whole thickness thereof (i.e., a height of the side wall 17 of the
electrode layer 15B) is usually 0.5-20 .mu.m, preferably 1-10
.mu.m.
[0061] The electrode layer 15A (as the substrate side electrode
layer) is formed substantially all over the first face 71A on the
side of the light-transmissive electroconductive member 20A among
the surfaces 71 of the LED body 11.
[0062] The electrode layer 15B (the light-emitting side electrode
layer) is formed in a smaller size than, e.g. 10 to 30% of, the
second face 71B of the LED body 11 so that luminescence is not
substantially obstructed. In other words, the electrode layer 15B
of the LED chip 10 is made smaller in areal size than the second
face 71B of the LED body 11 on which this electrode layer 15B is
formed. Incidentally, a transparent electrode layer can be present
between the LED body 11 and the electrode layer 15B.
[0063] Generally, unevenness is formed on the first face 71A of the
semiconductor substrate 41 on which the electrode layer 15A is
formed, and as a result, a corresponding unevenness 45 is given to
the electrode layer 15A laminated on it, thereby an improvement in
connection with a contiguous layer is achieved. The unevenness 45
on the surface of the electrode layer 15A is formed of concavities
46 and concavities 47 of the electrode layer 15A.
[0064] Generally, the unevenness 45 of the electrode layer 15A is
formed in order to improve the adhesion with the contiguous
electroconductive layer, and a surface roughness Ra (a measuring
method thereof is mentioned later) of usually 1-5 .mu.m is given
thereby. Incidentally, a surface roughness Ra of unevenness (not
shown) of the surface of the electrode layer 15B is usually 0.1-1
.mu.m.
[0065] The unevenness may be formed as a succession of concavities
and convexities, or may be given by intermittent formation of
concavities and/or convexities as by embossing. The surface
roughness Ra of the unevenness of the surface of the electrode
layers 15A and 15B can be 0.1 .mu.m-10 .mu.m.
[0066] The structures and materials of the semiconductor substrate
41, the P-type semiconductor layer 44 and N-type semiconductor
layer 42 of the LED chip 10, and the characteristics of the LED
chip 10 are not limited as long as desired luminescent performance
is acquired. Moreover, it is also possible that the semiconductor
substrate is a P-type or N-type semiconductor and/or the P-type
semiconductor layer 44 and N-type semiconductor layer 42 are
disposed upside down. However, it is desirable that the
semiconductor substrate has a semiconductor type opposite to that
of a semiconductor layer contiguous thereto, in view of the
luminous efficiency.
[0067] The LED chip 10 may comprise an LED chip emitting, e.g. red
or orange light, but may comprise an LED chip emitting another
color of light or a combination of the LED chips emitting plural
luminescence colors.
[0068] The LED chip 10 may ordinarily have a thickness (height) of,
e.g. 90-290 .mu.m, while it is not restricted in particular.
Moreover, although the surface size of the LED chip 10 may
naturally change variously with a requirement as a display element
(unit) for constituting the whole area of the light-emitting
device, it is usually in the range of 0.04 .mu.m.sup.2-2.25
mm.sup.2.
<Light-Transmissive Electroconductive Member>
[0069] The light-transmissive electroconductive member 20 (20A,
20B) comprises a transparent substrate 21 (21A, 21B) having
flexibility, and a light-transmissive electroconductive layer 25
(25A, 25B) formed on the surface of the transparent substrate 21. A
pair of the light-transmissive electroconductive members 20
sandwich the LED chip 10 so that the light-transmissive
electroconductive layers 25 thereof are electrically connected to
the electrode layers 15 (15A, 15B) of the LED chip 10. The
light-transmissive electroconductive layers 25 each form a circuit
pattern for driving at least one LED chip 10 of one or plural
types.
[0070] More specifically, the light-transmissive electroconductive
members 20 includes a first light-transmissive electroconductive
member 20A covering the LED chip 10 so that the light-transmissive
electroconductive layer 25A is electrically connected to the
surface of the first electrode layer 15A of the LED chip 10, a
second light-transmissive electroconductive member 20B covering the
LED chip 10 so that the light-transmissive electroconductive layer
25B is electrically connected to the surface of the second
electrode layer 15B of the LED chip 10.
[0071] [Transparent Substrate]
[0072] The transparent substrate 21 is a substrate which is
transparent or capable of light-transmission and flexible, and may
be in a sheet form. The transparent substrate 21 can also be in a
form of sheet having a curved surface as long as it retains
light-transmissivity and flexibility.
[0073] The transparent substrate 21 has a total light transmittance
(measured based on Japanese Industrial Standards JISK7375:2008) of
usually 90% or more, more preferably 95% or more, so as to provide
the light-emitting device of the present invention will have a
total light transmittance of usually 1%-80%, preferably 5 to 70%. A
higher total light transmittance provides a higher luminous
intensity of the light-emitting device and is generally preferred,
but a total light transmittance exceeding 80% may be undesirable,
since the circuit pattern of the light-transmissive
electroconductive member is liable to be recognized clearly. On the
other hand, a total light transmittance lower than 1% is not
desirable, since it becomes impossible to recognize each LED as a
luminescent spot.
[0074] The transparent substrate 21 may have a flexural modulus
(measured according to ISO178 (JIS K7171:2008)) of at least 150
kgf/mm.sup.2, preferably 200 to 320 kgf/mm.sup.2. The
light-emitting device 1 may be provided with a preferable degree of
flexibility if the transparent substrate 21 has a flexural modulus
in a range of from 150 kgf/mm.sup.2 to 320 kgf/mm.sup.2.
[0075] The transparent substrate 21, may comprise, e.g.
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polycarbonate (PC), polyethylene succinate (PES), "ARTON"
(registered trademark) available from JSR Corp., acrylic resin,
etc. The transparent substrate 21 may have a thickness of, e.g.
usually 50-300 preferably 50-200 .mu.m.
[0076] [Light-Transmissive Electroconductive Layer]
[0077] Although the material thereof is not particularly limited,
the light-transmissive electroconductive layer 25 may comprise,
e.g. a thick film comprising a light-transmissive resin binder
containing therein a plurality of light-transmissive
electroconductive fillers in a mutually contacting state; a thin
film of an electrical conductor material formed by sputtering or
vapor deposition; a mesh electrode comprising a non-light
transmissive conductor, such as silver-based fine particles; etc.
The light-transmissive electroconductive layer 25 is a layer which
has electroconductivity as well as light-transmissivity formed on
the surface of the transparent substrate 21. The light-transmissive
electroconductive layer 25 may have a transmittance of usually 10
to 85%.
[0078] More specifically, the light-transmissive electroconductive
layer 25, may comprise: (1) a conductor film formed by sputtering,
vapor deposition, etc., of light-transmissive conductors, such as
ITO (indium tin oxide), ZnO (zinc oxide), etc.; (2) an applied and
cured resin film of a slurry comprising particulates of
light-transmissive conductors, such as ITO, ZnO, etc. as mentioned
above, disperse in a light-transmissive resin (e.g.
ultraviolet-curable acrylic resin); (3) mesh electrodes, formed by
patterning through application, exposure and development of a
photosensitive compound, such as silver halide, of a
non-light-transmissive conductor such as Ag, patterning through
screen printing of Ag-based or Au-based fine particles, patterning
by laser irradiation or photo-etching, etc. of a film of a
non-light-transmissive conductor, such as Ag, Cu, etc., formed by
sputtering or electron beam vapor deposition; etc.
[0079] Among these, (1) has an advantage that a thin film electrode
having stable conductivity can be formed simply, but is liable to
have an inferior adhesion with a contacting light-transmissive
elastomer, thus being liable to result in an inferior flexural
resistance. In contrast thereto, (2) and (3) provide light-emitting
devices with good flexural resistance, and particularly (2) shows
especially good performance in this respect but is accompanied with
a difficulty that the electroconductivity thereof is liable to
change after standing for a long period at relatively high
temperatures (e.g. about 100.degree. C.). Although (3) is good in
balance of flexural resistance and electric conduction stability,
it involves difficulties in troublesome processing and a rather low
conductivity level attained. Therefore, it is desirable to effect
an appropriate selection from these, depending on the purpose,
manner of use, etc. of the light-emitting device obtained.
[0080] The thus-obtained light-transmissive electroconductive layer
25 may generally have a total light transmittance of 10 to 85% and
a sheet resistivity (according to a method described later) of at
most 1000 ohm/.quadrature.. Particularly, in view of the respective
characteristics of (1)-(3) described above, it is preferred that
the conductor film (1) is formed in a thickness of 0.05-2 .mu.m and
has a sheet resistivity of 10-500 ohm/.quadrature., particularly
10-50 ohm/.quadrature..
[0081] On the other hand, it is preferred that the coating
film-type electroconductive layer (2) contains particulate
conductor-dispersed therein, such as bar- or plate-shaped
light-transmissive particulate (filler) conductors, such as ITO,
ZnO, etc., having an average particle size (measured by laser
diffractometry according to ISO13320-1 (JIS Z8825-1)) of 10-200 nm,
especially 20-100 nm, and an aspect ratio (longer axis
diameter/shorter axis or thickness) of at least 2 dispersed in a
proportion of at least 50 wt. % and at most 95 wt. % or at most 90
wt. %, within a transparent binder of an acrylic resin, etc. and is
formed to have a total light transmittance of at least 80%,
particularly 85-99%, to have a thickness of 0.5-10 .mu.m,
particularly 1-5 .mu.m, and a sheet resistivity of 10-500
ohm/.quadrature., particularly 10-50 ohm/.quadrature..
[0082] The particulate conductor-dispersed film-type
electroconductive layer (2) shows electroconductivity represented
by the above-mentioned sheet resistivity because the conductor fine
particles (filler) dispersed therein are present in a mutually
contacting state. For this purpose, it is desirable that the
light-transmissive electroconductive filler particles are contained
in the light-transmissive electroconductive layer at a rate of at
least 50 wt. % and at most 95 wt. %.
[0083] If the coating-type light-transmissive electroconductive
layer 25 has a thickness less than 0.5 .mu.m, the layer is liable
to have a region comprising only a light-transmissive binder having
no conductivity so that the light-transmissive electroconductive
layer 25 is liable to have an excessively large sheet resistivity.
Moreover, if the light-transmissive electroconductive layer 25 has
a thickness less than 0.5 .mu.m, the layer is caused to have a
lower strength and inferior deformation followability, so that the
light-transmissive electroconductive layer 25 is liable to be
broken where the layer is bent at a large degree by being abutted
to an angular part such as an edge of the electrode layer 15 of the
LED chip 10. On the other hand, if the thickness of the
light-transmissive electroconductive layer 25 exceeds 10 .mu.m, the
formation thereof becomes difficult because of too large a
thickness and the layer is liable to be broken due to bending.
[0084] The light-transmissive electroconductive layer 25 has a
flexural resistance and deformation followability because the
conductor fine particles (filler) dispersed therein are mutually
bonded with the light-transmissive resin binder.
[0085] On the other hand, the light-transmissive electroconductive
layer of the mesh-type (3) is preferably formed as a mesh of a
non-light-transmissive conductor, such as Au or Ag, in a line
thickness having a cross-sectional area-equivalent diameter of 2-20
.mu.m and at a spacing of 100-1000 .mu.m so as to provide a total
light transmittance of 10 to 85%, and a sheet resistivity of 0.1-50
ohm/.quadrature., especially 0.1-10 ohm/.quadrature..
[0086] Au, etc., forming the mesh electrode is a
non-light-transmissive material, but as the mesh electrode occupies
only a small areal percentage, it provides a mesh electrode which
shows the above-mentioned level of total light transmittance as a
whole.
[0087] The light-transmissive electroconductive layer 25 according
to any of the above-mentioned compositions (1)-(3) may be
patterned, by a method, such as laser processing, etching, etc.,
into an electroconductive layer 25A connected to the electrode
layer (cathode) 15A on the N-type semiconductor layer 42, or an
electroconductive layer 25B connected to the electrode layer
(anode) 15B on the P-type semiconductor layer 44.
<Light-Transmissive Elastomer Layer>
[0088] The light-transmissive elastomer layer 30 comprises an
elastomer and is bonded to the circumference 13 of the LED chip 10
and the surfaces of the light-transmissive electroconductive layers
25 (25A, 25B) of the light-transmissive electroconductive member 20
(20A, 20B), thereby binding the LED chip 10 with the
light-transmissive electroconductive members 20 (20A, 20B).
[0089] Thus, in an arrangement that the LED chip 10 is sandwiched
between the light-transmissive electroconductive layer 25A side of
the light-transmissive electroconductive member 20A and the
light-transmissive electroconductive layer 25B side of the
light-transmissive electroconductive member 20B, the
light-transmissive elastomer layer 30 is disposed to fill up a
space or region which is formed between the light-transmissive
electroconductive member 20A and the light-transmissive
electroconductive member 20B and surrounds the peripheral wall 13
of an LED chip.
[0090] More specifically, the light-transmissive elastomer layer 30
also fills up a gap space or crevice gap 48 formed between
concavities 46 of the surface unevenness 45 of the electrode layer
15 of the LED chip 10 and the surface 26 of the light-transmissive
electroconductive layer 25A of the light-transmissive
electroconductive member 20A. Thus, if the gap space 48 is also
filled up with the light-transmissive elastomer layer 30, the
light-transmissive electroconductive layer 25A of the
light-transmissive electroconductive member 20A becomes free from
cracking, and the electrode layer 15 of the LED chip 10 and the
light-transmissive electroconductive layer 25A of the
light-transmissive electroconductive member 20A are bonded firmly,
so that firm electrical connection and therefore a lighting state
are retained even if the light-emitting device 1 is subjected to
intense bending or application of heat cycle.
[0091] FIG. 5 shows an example of scanning electron microscope
photograph showing a surface of the first electrode layer 15A of Au
of the LED chip 10 after peeling between the first electrode layer
15A and the first light-transmissive electroconductive member
20A.
[0092] FIG. 5 shows a state where the light-transmissive elastomer
layer 30 adheres firmly to the surface of the electrode layer 15A
along or even more with the surface unevenness of the first
electrode layer 15A of the LED chip 10 after the peeling. FIGS. 6A
to 6C show surface states of a first electrode layer 15A of the LED
chip 10 after peeling between the first electrode layer 15A and a
first light-transmissive electroconductive member 20A in a
light-emitting device according to the first embodiment; among
which FIG. 6A is a scanning electron microscope photograph, FIG. 6B
is an elemental mapping photograph for carbon according to energy
dispersion-type X-ray analysis (EDX), and FIG. 6C is an elemental
mapping photograph for tin according to EDX.
[0093] In view of these figures, it is shown that element tin
(originated from an ITO-dispersed electroconductive layer 25A) is
hardly observed in a region where element C (elastomer 30 origin)
is frequently observed on the surface of the first electrode layer
15A of the LED 10, while element C is little observed where much
element tin is present. FIGS. 6A-6C are shown at a magnification of
250 times, and have been taken at an electron beam accelerating
voltage of 15.0 kV. Numerals indicated at an upper part of FIG. 6A
represent a gray scale of the SEM secondary electron image and the
gray scale indicated with numerals at upper parts of FIGS. 6B and
6C represent atomic percentages of elements C (carbon) and Sn
(tin), respectively, on the observed face. Incidentally, FIGS.
6A-6C can be observed as color pictures and the atomic % can be
recognized not by a gray scale but as a color change, at the time
of actual measurement.
[0094] In FIGS. 6A-6C, the region where much tin is observed with
almost no C, represents a region (region a) where the first
electrode layer 15A of the LED chip 10 and the first
light-transmissive electroconductive layer 25A (represented by the
light-transmissive electroconductive filler ITO contained therein)
contacted directly with each other. Here, the tin observed in FIG.
6C shows that the light-transmissive electroconductive filler
containing tin in the layer 25A was transferred to the first
electrode layer 15A at the time of peeling between the first
electrode layer 15A and the first light-transmissive
electroconductive layer 25A. These results show that a good
electrical connection was established between the first electrode
layer 15A and the first light-transmissive electro-conductive layer
25A of the LED chip 10.
[0095] In FIGS. 6A-6C, the region where much carbon is observed
with almost no tin on the first electrode layer 15A of the LED chip
10, represents a region (region b) where the light-transmissive
elastomer layer 30 enters between the first electrode layer 15A of
the LED chip 10 and the first light-transmissive electroconductive
layer 25A to mechanically join the first electrode layer 15A and
the first light-transmissive electroconductive layers 25A of the
LED chip 10. Thus, it has been found because of the co-presence of
the region a and the region b that, in the light-emitting device of
the present invention, an electrical connection and mechanical
junction are both satisfactorily maintained between the first
electrode layer 15A and the first light-transmissive
electroconductive layer 25A of the LED chip 10.
[0096] Moreover, although an unevenness finer than unevenness 45 of
the surface of the electrode layer 15A is usually present on the
surface of the electrode layer 15B of the LED chip 10, the
light-transmissive elastomer layer 30 is formed also in the minute
gap space between the minute surface unevenness of the electrode
layer 15B and the surface of the light-transmissive
electro-conductive layer 25B of the light-transmissive
electroconductive member 20B. Furthermore, on the electrode-layer
15B side, the light-transmissive elastomer exists abundantly near
the center of the electrode layer, and, as for an electrode
peripheral part, there is clearly observed a trace that the
electrode and the light-transmissive electroconductive layer
touched directly with each other. Thus, if the light-transmissive
elastomer layer 30 is formed also in the minute crevice space on
the surface of the light-transmissive electroconductive layer 25B
and the light-transmissive elastomer is also present in the other
region, the light-transmissive electroconductive layer 25B of the
light-transmissive electroconductive member 20B is less liable to
be cracked, and the electrode layer 15 of the LED chip 10 and the
light-transmissive electroconductive layer 25B of the
light-transmissive electroconductive member 20B are bonded firmly,
so that an electrical connection and therefore a lighting state are
firmly kept even under severe bending and application of a thermal
cycle.
[0097] The present inventor peeled the light-transmissive
electroconductive members apart from the LED chips of the
light-emitting devices and measured an areal percentage of a region
on an LED electrode where a carbon atomic % is at least 50% with
respect to the area of the LED electrode after the peeling based on
planar carbon analysis according to the EDX observation (hereafter
called an "elastomer coverage (on an LED electrode)" and a
measuring method therefor is described later). As a result, the
present inventor has found that good electrical connection and
mechanical junction are realized when the elastomer coverage is
10-90%, preferably 20-80%, both on the LED electrodes 15A and 15B,
and also has found a solution for realizing the condition.
[0098] The light-transmissive elastomer layer 30 is a layer of an
elastomer having a light-transmissivity but no electroconductivity,
and has a total light transmittance of 1 to 99%, preferably 5 to
90%.
[0099] The Vicat softening temperature (of which the measuring
method is mentioned later) of the elastomer for the
light-transmissive elastomer layer 30 is preferably 80.degree. C.
to 160.degree. C., more preferably 100.degree. C. to 140.degree. C.
Moreover, the tensile storage modulus of the elastomer for the
light-transmissive elastomer layer 30 is in the range of preferably
0.01 to 10 GPa, more preferably 0.1 to 7 GPa, respectively between
0 to 100.degree. C.
[0100] It is preferred that the elastomer used for the
light-transmissive elastomer layer 30 does not melt at the Vicat
softening temperature, and shows a tensile storage modulus at the
Vicat softening temperature of at least 0.1 MPa, and a melting
temperature which is at least 180.degree. C., more preferably
200.degree. C. or more, or is higher than Vicat softening
temperature by at least 40.degree. C., more preferably by
60.degree. C. or more. The glass transition temperature of the
elastomer used for the light-transmissive elastomer layer 30 is
preferably at most -20.degree. C., more preferably -40.degree. C.
or below.
[0101] An elastomer is an elastic polymer material and is a resin.
The elastomer used here is a thermoplastic elastomer as is
understood from the fact that it has a Vicat softening temperature.
It is a polymer which shows rubber elasticity, e.g. around room
temperature and shows thermoplasticity at higher temperatures.
Thermoplastic elastomer can be of a type which is polymerized on
temperature increase up to a curing temperature and has
thermoplasticity thereafter. The production process of the
light-emitting device according to an embodiment of the present
invention is characterized in that such a thermoplastic elastomer
sheet in a state of being inserted between the LED chip electrode
and the electroconductive layer is subjected to a vacuum press at a
temperature which is equivalent to or slightly above the Vicat
softening point and below the melting temperature, thereby
deforming the elastomer sheet without causing excessive plasticity
or flowing to fill the gaps between the LED chip electrode and the
electroconductive layer and improve the bonding (peeling
prevention) and electric connection between the LED chip electrode
and the electroconductive layer.
[0102] Examples of the elastomer used for the light-transmissive
elastomer layer 30, may include an acrylic elastomer, an olefinic
elastomer, a styrene-based elastomer, an ester-based elastomer, a
urethane-base elastomer, etc.
[0103] It is possible to contain another resin component, filler,
additive, etc., if needed.
[0104] In order to improve the filling effect of the elastomer in
the product light-emitting device and to secure a contact between
the LED chip electrode and the electroconductive layers, it is
desirable that the thickness of the light-transmissive elastomer
layer 30 is equal to or below the thickness of the LED chip 10. The
light-transmissive elastomer layer 30 may have an upper limit
thickness which is preferably smaller by at least 5 .mu.m, more
preferably smaller by at least 10 .mu.m, still more preferably
smaller by at least 20 .mu.m, than the thickness (height) of the
LED chip 10. Moreover, the light-transmissive elastomer layer 30
may have a lower limit thickness which is usually 1/2, preferably
3/5, of the thickness of the LED chip 10.
[0105] Here, the thickness of the light-transmissive elastomer
layer 30 refers to a thickness of the light-transmissive elastomer
layer 30 measured at a part which is separated 100 .mu.M or more
from the peripheral wall of the LED body 11 of the LED chip 10 and,
in a region between the neighboring LEDs, a thickness of the
light-transmissive elastomer layer 30 at a thinnest part between
the LEDs. This thickness usually does not differ substantially from
the total thickness of a pair of elastomer sheets disposed over the
upper and lower faces of the LED chip before the vacuum
pressing.
<Production Process>
[0106] A production process for the light-emitting device 1 (FIG.
1) is explained with reference to FIG. 7.
[0107] For production of a light-emitting device 1,
light-transmissive-elastomer sheets 35 are placed between electrode
layers 15 of an LED chip 10 and light-transmissive
electroconductive layers 25 of light-transmissive electroconductive
members 20, and a preliminary press is performed at a weak
pressure, to form a temporary laminate. Then, a working environment
is evacuated to a vacuum. In such a vacuum environment, the
temporary laminate is pressure-bonded at a temperature (Tp) which
is lower by at most 10.degree. C. and higher by at most 30.degree.
C., preferably by at most 20.degree. C., than the Vicat softening
point (Tv) of the light-transmissive elastomer (i.e., Tv-10.degree.
C..ltoreq.Tp.ltoreq.Tv+30.degree. C., more preferably Tv-10.degree.
C..ltoreq.Tp.ltoreq.Tv+20.degree. C.).
[0108] In addition, the tensile storage modulus at the Vicat
softening temperature of the elastomer used for the
light-transmissive elastomer layer 30, is desirably at least 0.1
MPa, more preferably at least 1 MPa, e.g. 1 MPa-1 GPa.
[0109] Moreover, the tensile storage modulus at the heat
pressure-bonding temperature of the elastomer used for the
light-transmissive elastomer layer 30, is desirably at least 0.1
MPa, more preferably at least 1 MPa, e.g. 1 MPa-1 GPa.
[0110] The desirable ranges for the Vicat softening temperature,
the tensile storage modulus at the hot pressure-bonding temperature
and other parameters described above also hold true with other
embodiments disclosed herein.
[0111] [Lamination and Vacuum Hot Pressing]
[0112] More specifically, with reference to FIG. 7, a
light-transmissive-elastomer sheet 35 of a predetermined thickness
is disposed on a light-transmissive electroconductive layer 25B of
a light-transmissive electroconductive member 20B so as to cover
the entirety of the light-transmissive electroconductive layer 25B,
and one or more LED chips 10 are arranged at predetermined position
and in a predetermined direction on the
light-transmissive-elastomer sheet 35 so as to provide a desired
display pattern in a resultant light-emitting device. Further
thereon, a light-transmissive-elastomer sheet 35 of a predetermined
thickness is disposed, and thereon, a light-transmissive
electroconductive member 20A is disposed at a predetermined
position while directing its light-transmissive electroconductive
layer 25A downward. The light-transmissive-elastomer sheet has a
shape which covers the entirety of the light-transmissive
electro-conductive layer 25A. The above-described order of
lamination can be reversed upside down.
[0113] Next, the resultant laminate is subjected to a preliminary
press, and the working environment is made vacuum. In such a vacuum
atmosphere, pressing is performed for a predetermined period of,
e.g. 20 to 60 minutes while heating the laminate. The heating
temperature for the vacuum hot pressing is, e.g. usually
80-180.degree. C., preferably 100-160.degree. C. The degree of
vacuum (absolute pressure) for the vacuum hot pressing is, e.g.
usually at most 10 kPa, preferably 5 kPa or less. The pressure
applied for the vacuum hot pressing is, e.g. usually 0.5-20 MPa
(5-200 kgf/cm.sup.2), preferably 0.6-12 MPa (6-120
kgf/cm.sup.2).
[0114] As a result, the light-transmissive-elastomer sheets 35 in
the laminate are softened to envelope the LED chip 10 while
preventing the crack or fracture due to pressurization of the
light-transmissive electroconductive layers, and the softened
light-transmissive elastomer layers are bonded and unified with
each other to form a light-transmissive elastomer layer 30.
Simultaneously therewith, the electrodes of the LED chip and the
light-transmissive electroconductive layers mutually contact and
take electric connection with each other. Vacuum hot pressing is
performed so that the thickness of the light-transmissive elastomer
layer 30 may become smaller than the thickness of the LED chip 10.
At the end of the vacuum hot pressing, a light-emitting device 1 as
shown in FIG. 1 is obtained.
[0115] During the vacuum hot pressing, stress is locally added to
the light-transmissive electroconductive layers 25 of the
light-transmissive electroconductive members 20 as they contact the
electrode layers 15 of the LED chip 10. More specifically, a thrust
from the convexities 47 of the electrode layer 15A of the LED chip
10 is added to the light-transmissive electroconductive layer 25A
of the light-transmissive electroconductive member 20A, as shown in
FIG. 2. Moreover, the light-transmissive electroconductive layer
25B of the light-transmissive electroconductive member 20B receives
a thrust from convexities constituting the unevenness 45 on the
electrode layer 15B of the LED chip 10 and a thrust from the angle
part 18 of the electrode layer 15B of the LED chip 10.
[0116] However, when the elastomer laminate shown in FIG. 7 is
pressed in the direction of arrows P, the crevice space or gap 48
(FIG. 2) between the surface of the electrode layer 15 (15A, 15B)
of the LED chip 10 and the light-transmissive electroconductive
layer 25 (25A, 25B) of the light-transmissive electroconductive
member 20 (20A, 20B) is filled up with the light-transmissive
elastomer layer 30 formed with the softened elastomer sheets 35, so
that the occurrence of crack and fracture of the light-transmissive
electroconductive layer 25 of the light-transmissive
electroconductive member 20 possibly caused by the thrusts from the
convexities of the unevenness 45 on the surface of the electrode
layer 15 (15A, 15B) of the LED chip 10, is suppressed.
[0117] Moreover, the light-transmissive electroconductive layer 25
(25A, 25B) of the light-transmissive electroconductive member 20
comprises light-transmissive-electroconductive-filler particles and
a light-transmissive resin binder for binding
light-transmissive-electroconductive-filler particles while keeping
mutual contact between the adjacent particles, and has flexibility
or followability to deformation. For this reason, even if local
thrust is applied to the light-transmissive electroconductive layer
25 of the light-transmissive electroconductive member 20 from the
convexities 47 of the electrode layer 15A of the LED chip 10, or
from the angle part 18 of the electrode layer 15B, a fatal crack in
the light-transmissive electroconductive layer 25 is hardly caused
and, even if a crack arises, a lighting state can be maintained,
since the electric connection reliability of the light-transmissive
electroconductive layer is high owing to the presence of the
light-transmissive resin binder. Further, the resultant
light-emitting device 1 hardly causes a fatal crack when it is
severely bent and, even if a crack arises, a lighting state can be
maintained, since the light-transmissive resin binder maintains the
electric connection of the light-transmissive electroconductive
layer.
[0118] The control the above-mentioned elastomer coverage in a
desirable range may be achieved to some extent by appropriately
controlling the total thickness of the light-transmissive elastomer
layers 35 within the range of, e.g. 40 to 99%, preferably 60 to
85%, of the thickness (height) of the LED chip 10, but in addition
thereto, it is desirable to adjust the shape, material and
cushioning properties of the press machine surface contacting the
light-transmissive electroconductive member 20 during the vacuum
hot pressing, and the conditions of the vacuum hot pressing, such
as temperature, pressure and timing. The combination of concrete
conditions can be suitably chosen depending on the design of a
light-emitting device, and the design of vacuum hot pressing
apparatus.
[0119] The local intrusion or penetration of the light-transmissive
elastomer layer 30 between the electrode layer 15 of the LED chip
10 and the transparent electroconductive layer 25, may be performed
by methods other than above-mentioned manufacturing process, such
as a method of disposing granular or pillar-shaped
light-transmissive elastomer of a suitable size on the electrode
layer 15 of the LED chip 10, followed by a step of vacuum hot
pressing; and a method of applying or spraying the emulsion of
light-transmissive-elastomer powder on the transparent
electroconductive layer 25 or the electrode layer 15 of the LED
chip 10, followed by drying thereof and vacuum hot pressing, and
the production process is not limited to the above-mentioned
process. However, in view of the ease of production, the
above-mentioned production process is excellent.
[0120] [Effect of the Production Process]
[0121] According to the production process, the light-emitting
device 1 is easily producible. Moreover, since the LED chip 10 is
sandwiched by the light-transmissive elastomer layers 35, the LED
chip 10 can be reliably fixed for the production.
<Function>
[0122] The function of the light-emitting device 1 is
explained.
[0123] In the light-emitting device 1, the light-transmissive
elastomer layer 30 is formed also in the crevice space 48 between
the concavities 46 of the unevenness 45 on the surface of the
electrode layer 15 (15A, 15B) of the LED chip 10, and the surface
26 of the light-transmissive electroconductive layer 25 (25A, 25B)
of the light-transmissive electroconductive member 20 (20A, 20B),
so that the light-transmissive electroconductive layer 25 (25A,
25B) hardly causes a crack or a fracture, even if the convexities
47 of the unevenness 45 on the surface of the electrode layer 15
(15A, 15B) of the LED chip 10 abut onto the surface 26 of the
light-transmissive electroconductive layer 25 (25A, 25B) of the
light-transmissive electroconductive member 20 (20A, 20B). As a
result, the electric connection reliability of the
light-transmissive electroconductive layer becomes high, so that a
lighting state can be maintained, even if the light-emitting device
1 is bent severely or subjected to a thermal cycle.
[0124] Moreover, in the light-emitting device 1, the
light-transmissive elastomer layer 30 is formed also in the crevice
space 48 between the concavities 46 of the unevenness 45 on the
surface of the electrode layer 15 (15A, 15B) of the LED chip 10,
and the surface 26 of the light-transmissive electroconductive
layer 25 (25A, 25B) of the light-transmissive electroconductive
member 20 (20A, 20B), so that a positional deviation is hardly
caused in the direction of extension of the boundary between the
electrode layer 15 of the LED chip 10, and the light-transmissive
electroconductive layer 25 of the light-transmissive
electroconductive member 20. For this reason, the electric
reliability of the light-emitting device 1 is high.
[0125] Furthermore, since the light-transmissive electroconductive
layer 25 of the light-emitting device 1 is formed by binding a
multiplicity of light-transmissive electroconductive fillers with a
light-transmissive resin binder, the light-transmissive
electroconductive layer 25, as a whole, shows a flexural resistance
or followability to deformation. Thus, even when the
light-transmissive electroconductive layer 25 is bent along with an
edgy part, such as an angle portion of the electrode layer 15, the
light-transmissive resin binder portion binding a
light-transmissive electroconductive filler bends or deforms, so
that the light-transmissive electroconductive layer 25 is rich in
followability to such an edgy part like an angle portion of the
electrode layer 15. For this reason, when the light-transmissive
electroconductive layer 25 is severely bent along with an edgy
part, such as an angle part of the electrode layer 15, e.g. during
production of the light-emitting device 1, a fatal crack hardly
occurs in the light-transmissive electroconductive layer 25 so that
lighting ability is maintained by retaining electric connection of
the light-transmissive electroconductive layer with the
light-transmissive resin binder. Incidentally, although the
unevenness 45 is shown only on the electrode layer 15A of the LED
chip 10 in FIG. 2, similar unevenness is actually present also on
the electrode layer 15B.
<Comparative Manufacturing Processes>
[0126] The production process according to this embodiment is
characterized by the features that (1) for providing an electric
connection between the LED electrode layer 15 and the
light-transmissive electroconductive layer 25, an elastomer sheet
35 that does not melt or have a low viscosity (meant herein to
assume a tensile storage modulus less than 0.1 MPa) during the
vacuum hot pressing step is inserted between the LED electrode 15
and the light-transmissive electroconductive layer 25, and (2) the
laminate including the light-transmissive electroconductive member
20, the elastomer sheet 35 and the LED chip 10, is subjected to
vacuum hot pressing.
[0127] [A Manufacturing Process Wherein Vacuum Hot Pressing is
Performed without Inserting an Elastomer Between an LED Electrode
and a Light-Transmissive Electroconductive Member]
[0128] An example of production not satisfying the feature (1)
performed by the present inventor is explained.
[0129] FIG. 8 illustrates Production example 1 for a light-emitting
device which was performed by forming a laminate consisting of
light-transmissive electroconductive members 20, an elastomer sheet
35 and an LED chip 10 without inserting a
light-transmissive-elastomer sheet 35 between the electrode layer
15A of the LED chip, and the light-transmissive electroconductive
layer 25A, and subjecting the resultant laminate to vacuum hot
pressing, otherwise in a similar manner as in the above-mentioned
first embodiment for production of the light-emitting device 1.
[0130] FIG. 9 illustrates Production example 2 for a light-emitting
device which was performed by forming a laminate consisting of
light-transmissive electroconductive members 20, an elastomer sheet
35 and the LED chip 10 without inserting a
light-transmissive-elastomer sheet 35 between the electrode layer
15B of an LED chip, and the light-transmissive electroconductive
layer 25B, and subjecting the resultant laminate to vacuum hot
pressing, otherwise in a similar manner as in the above-mentioned
first embodiment for production of the light-emitting device 1.
[0131] A light-emitting device 90 produced by Production example 1
and a light-emitting device 90A produced by Production example 2
are explained below.
[0132] FIG. 10 is a partial enlarged view of a section of the
light-emitting device 90 produced by Production example 1. FIG. 11
is a partial enlarged view of section B1 in FIG. 10. FIG. 12 shows
an example of cross-sectional photograph of the light-emitting
device 90 of the light-emitting device 90 produced by Production
example 1. FIG. 13 shows an example of cross-sectional photograph
of the light-emitting device 90A produced by Production example
2.
[0133] (Luminescent Device 90 of Production Example 1)
[0134] As shown in FIG. 10-FIG. 12, in the light-emitting device 90
obtained by Production example 1, the crevice gap 48 formed between
the concavity 46 of the unevenness 45 of the surface of the
electrode layer 15 of the LED chip 10 and the surface 26 of the
light-transmissive electroconductive layer 25A of the
light-transmissive electroconductive member 20A serves as a vacant
gap 91, and the light-transmissive elastomer 30 is hardly present
there. Thus, the elastomer coverage was clearly below 10%.
[0135] As a result of a bending resistance test and a thermal
cycling test, the light-emitting device 90 readily caused a
lighting failure. As shown in FIG. 11, a crack 92 was caused at a
part, of the light-transmissive electroconductive layer 25A of the
light-transmissive electroconductive member 20A, abutting the
convexity 47 of the electrode layer 15A of the LED chip 10. This is
presumably because the stress from the convexity 47 concentrated
under severe bending, leading to the lighting failure under
application of bending and thermal cycles.
[0136] (Second Light-Emitting Device 90A of Production Example
2)
[0137] FIG. 13 is a scanning electron microscope photograph of a
section of a laminate after vacuum hot pressing of the laminate
consisting of the light-transmissive electroconductive member 20,
the elastomer sheet 35 and the LED chip 10 without inserting the
light-transmissive elastomer sheet 35 between the electrode layer
15B of an LED chip and the light-transmissive electroconductive
layer 25B.
[0138] As shown in FIG. 13, in the light-emitting device 90A, there
occurred a vacant gap 91 around the electrode layer 15B of the LED
chip 10, where almost no light-transmissive elastomer layer 30 was
present in the vacant gap 91. Thus, the elastomer coverage was
clearly below 10%.
[0139] For this reason, as a result of the bending resistance test
and thermal cycling test, the light-emitting device 90A readily
caused a lighting failure. This is presumably because a crack
occurred at a part, of the light-transmissive electroconductive
layer 25B of the light-transmissive electroconductive member 20B,
abutting the angle part of the electrode layer 15B of the LED chip
10, and the stress from the angle part concentrated under severe
bending.
[0140] (Luminescent Device According to a Production Process of
Patent Document 5)
[0141] JP-A 2012-84855 (Patent document 5) discloses a process for
producing a light-emitting device, comprising: forming a
through-hole in an intermediate layer comprising an acrylic
elastomer, disposing a light-emitting element in the through-hole,
and sandwiching the front and back faces of the light-emitting
element with a pair of supports.
[0142] More specifically, there is disclosed a process, wherein an
acrylic elastomer sheet having a through-hole therein is placed in
contact on a first support, a light-emitting element is disposed in
the through-hole, a second support is disposed in contact on the
acrylic elastomer sheet, and the resultant laminate is sandwiched
and press-heated with a heating drum to produce a light-emitting
device.
[0143] In the light-emitting device manufactured by this process, a
vacant gap 91 occurred around the electrode layer 15 of the LED
chip 10, and almost no light-transmissive elastomer layer 30 was
present in the vacant gap 91, so that the elastomer coverage was
clearly below 10%. Moreover, many air bubbles remained near the LED
chip.
[0144] In the light-emitting device according to the production
process of Patent document 5, although the lighting was generally
realized in the initial state, lighting failure was caused as the
time passed in many cases. Moreover, lighting failure was readily
caused during the bending test and the thermal cycling test.
[0145] (Luminescent Device C According to a Production Process of
Patent Document 3)
[0146] Patent document 3 discloses a process wherein a hot melt
adhesive, instead of the light-transmissive elastomer sheet 35, is
disposed between the electrode layer 15 of an LED chip and the
light-transmissive electroconductive layer 25, and the resultant
laminate consisting of the light-transmissive electroconductive
member 20, the elastomer sheet 35 and the LED chip 10 is subjected
to hot pressing (while melting the hot melt adhesives). The
light-transmissive elastomer used in the production process of the
present invention is a material which needs to maintain the nature
of a light-transmissive elastomer in a vacuum hot pressing step,
and is a quite different material from a hot melt adhesive which is
a material that melts at a processing temperature and is
inapplicable to vacuum hot pressing.
[0147] As a result, the light-emitting device C according to Patent
document 3 was difficult to manufacture without leaving air bubbles
in the light-emitting device including a region between the
electrode layer 15 of the LED chip and the light-transmissive
electroconductive layer 25, so that a vacant gap not filled with
the hot melt adhesive remained between the electrode layer 15 of an
LED chip, and the light-transmissive electroconductive layer 25,
and also a crack occurred at a part where the light-transmissive
electroconductive layer 25 abutted the electrode layer 15
presumably during the pressing. For this reason, in the
light-emitting device 90C, lighting failure readily occurred during
the bending test or thermal cycling test.
Second Embodiment
[0148] FIG. 14 is a sectional view of a light-emitting device of a
second embodiment. Compared with the light-emitting device 1 shown
in FIG. 1 as a first embodiment, the light-emitting device 1A is
different in that it includes an LED chip 10A having two types of
electrodes 15A and 15B on one face thereof in place of the LED chip
10, a transparent substrate 21D having no light-transmissive
electroconductive layer 25 in place of the first light-transmissive
electroconductive member 20A, and a light-transmissive
electroconductive member 20C having two types of light-transmissive
electroconductive layers 25A and 25B in place of the second
light-transmissive electroconductive member 20B, and the other
structure is identical to the light-emitting device 1. Accordingly,
with respect to the light-emitting device 1A shown in FIG. 14 as a
second embodiment, the same components as those in the
light-emitting device 1 shown in FIG. 1 as a first embodiment are
denoted by identical symbols or numerals, and further explanations
of structure and function are omitted or simplified.
[0149] More specifically, the light-emitting device 1A includes: an
LED chip 10A having a first and a second electrode layer 15 (15A,
15B) on one face of an LED body 11A; a light-transmissive
electroconductive member 20C which includes a transparent substrate
21C and a first and a second light-transmissive electroconductive
layer 25 (25A, 25B) formed on the transparent substrate 21C and
covers the face having the electrode layers 15 of the LED chip 10A;
a transparent substrate 21D covering the other face of the LED chip
10A; and a light-transmissive elastomer layer 30 which consists of
an elastomer and is bonded to the circumference 13 of the LED chip
10A, the surface of the light-transmissive electroconductive member
20C, and the surface of the transparent substrate 21D.
[0150] In short, the light-emitting device 1A is formed by
sandwiching the LED chip 10A with the light-transmissive
electroconductive member 20C and the transparent substrate 21D, and
bonding the LED chip 10A, the light-transmissive electroconductive
member 20C and the transparent substrate 21D with the
light-transmissive elastomer layer 30.
<LED Chip>
[0151] FIG. 15 is an enlarged view of the LED chip 10A shown in
FIG. 14.
[0152] The LED chip 10A includes the electrode layer 15A as a first
electrode layer and the electrode layer 15B as a second electrode
layer formed on one face of the LED body 11A.
[0153] Compared with the LED chip 10 used in the light-emitting
device 1 as the first embodiment, the LED chip 10A differs in that
the electrode layer 15A and the electrode layer 15B are formed on
one face of the LED body 11A, and the other composition is the same
as the latter. Hereinbelow, only the differences between the LED
chip 10A and the LED chip 10 are explained.
[0154] The LED body 11A has an N-type semiconductor layer 42 and a
P-type semiconductor layer 44 on a substrate 41A made of, e.g. a
semiconductor or sapphire, a luminescence layer 43 is formed
between the N-type semiconductor layer 42 and the P-type
semiconductor layer 44.
[0155] A face on which the electrode layers 15A (cathode) and 15B
(anode) are formed among the faces 71 of the LED body 11A is called
a third face 71C of the LED body 11A. In this example, the third
face 71C of the LED body 11 is the surface of the P-type
semiconductor layer 44. The electrode layer 15B is formed on the
third face 71C.
[0156] Moreover, a face opposite to the third face 71C of the LED
body 11A and having no electrode layer 15A or 15B thereon is called
a fourth face 71D of the LED body 11. The fourth face 71D is a
surface of the LED substrate 41A. It is possible to dispose a
reflective film (not shown) on the surface of the LED substrate
41A, or on the face 71C. It is also possible that the face 71C or
the face 71D forms a luminescence face of LED chip 10. In case
where the LED substrate 41A is transparent, almost all the faces of
the LED chip 10A can be a luminescence face. Light can be taken out
from either one face or both faces, and a face close to the
luminescence layer 43 is hereafter called a luminescence face
herein for convenience.
[0157] The electrode layer 15A (cathode), in this example, is
formed on and electrically connected to a non-covered and exposed
face 72 of the N-type semiconductor layer 42 which is generally
covered with the luminescence layer 43 and the P-type semiconductor
layer 44. Since the exposed face 72 of the N-type semiconductor
layer 42 and the third face 71C of the LED body 11A are disposed in
an identical direction as viewed from the center of the LED body
11A, the electrode layer 15A is formed on the luminescence
layer-side interface 72 of the N-type semiconductor layer 42 and
also disposed on the third face 71C of the LED body 11A.
[0158] The electrode layer 15A and the electrode layer 15B may have
a thickness (height) of usually 0.1-10 .mu.m, preferably 1-5 and
their thicknesses are almost identical but can differ by about 1
.mu.m at the maximum. The electrode layer 15A and the electrode
layer 15B are usually formed in a total area which is smaller than
that of the face 71C of the LED body 11 so that luminescence may
not be obstructed.
[0159] A certain degree of unevenness is formed in the exposed face
72 of the N-type semiconductor layer 42 on which the electrode
layer 15A is formed. Accordingly, a similar form of unevenness as
the unevenness on the face 72 is formed in the surface of the
electrode layer 15A formed on the exposed face 72.
[0160] The unevenness of the surface of the electrode layer 15A and
the electrode layer 15B may respectively give a roughness of
preferably at least 0.1 .mu.m. As a result, the surfaces of the
electrode layers 15A and 15B may have a higher adhesiveness with
the light-transmissive electroconductive member 20C in the
light-emitting device of the present invention.
<Transparent Substrate>
[0161] The transparent substrate 21D is identical to the
transparent substrate 21A constituting the light-transmissive
electroconductive member 20A in the first embodiment, so that
explanation thereof is omitted.
<Light-Transmissive Electroconductive Member>
[0162] The light-transmissive electroconductive member 20C includes
a transparent substrate 21C having a flexural resistance, and two
types of light-transmissive electroconductive layers 25A and 25B
formed on one surface of the transparent substrate 21C. The
light-transmissive electroconductive layer 25A is formed so as to
be electrically connected to the electrode layer 15A of the LED
chip 10A, and the light-transmissive electroconductive layer 25B is
formed so as to be electrically connected to the electrode layer
15B of the LED chip 10A.
[0163] Compared with the light-transmissive electroconductive
member 20B used in the light-emitting device 1 as the first
embodiment, the light-transmissive electroconductive member 20C
differs in that the light-transmissive electroconductive layer 25A
and the light-transmissive electroconductive layer 25B are formed
on one surface of the transparent substrate 21C, and the other
composition is identical.
[0164] The light-transmissive electroconductive layer 25 formed on
the light-transmissive electroconductive member 20C, similarly as
the light-transmissive electroconductive layer 25 in the first
embodiment, may be any form of (1) a conductor thin film, (2) a
resin film containing fine particles of light-transmissive
conductor dispersed therein, and (3) a mesh electrode. The
light-transmissive electroconductive layer 25 formed on the
transparent substrate 21C in a form of (1)-(3) above, may be
patterned into the electroconductive layer 25A connected to the
electrode layer (cathode) 15A on the N-type semiconductor layer 42,
or the electroconductive layer 25B connected to the electrode layer
(anode) 15B on the P-type semiconductor layer 44, by laser
processing, etching processing, etc.
[0165] The electrode layers 15A and 15B of the LED chip 10A are
formed as so-called "pad electrodes" of a metal conductor, such as
Au, and they are electrically connected to the light-transmissive
electroconductive layers 25A and 25B, respectively, after
positional alignment and vacuum pressing. When the thus-obtained
light-emitting device was subjected to repetitive bending, the
occurrence of lighting failure was observed. As a result of study
thereafter, it was found that the failure was caused when the
device in a state as shown in FIG. 14 was bent convex upwards to
cause the touching of a front end of the light-transmissive
electroconductive layer 25A connected to the electrode layer 15A
(cathode) with the electrode 15B (anode), thus causing a
cathode-anode short-circuit. Moreover, according to a further
study, this inconvenience could be avoided by locally forming a
bump electrode of a good conductor, such as Au or Ag, of about
50-100 .mu.m in both diameter and height on each of the pad
electrodes 15A and 15B of the LED chip 10A, and connecting the bump
electrodes to the light-transmissive electroconductive layers 25A
and 25B, respectively. The short circuit prevention effect by
formation of such a bump electrode on a pad electrode can be also
attained in the first embodiment of using an LED chip having
electrodes on both faces thereof by forming such a bump electrode
on a pad electrode having a smaller area than LED chip (the anode
electrode 15B in the example of FIG. 1).
[0166] FIGS. 17 and 18 are schematic cross sectional views of
light-emitting devices 1AA and 1BA which may be prepared by forming
such bump electrodes 36A and 36B, and a bump electrode 36, in the
light-emitting devices of FIG. 14 and FIG. 1, respectively. Such a
bump electrode 36A, 36B or 36 may be formed as follows.
[0167] A tip of, e.g. Au wire, is discharged by using a wirebonding
apparatus to form an Au bump 36S on a pad electrode 15 (15A, 15B)
of an LED chip, e.g. as shown in FIG. 19, the Au bump 36 is
preferably pressed to flatten the top A, and then over the LED
chip, the above-mentioned light-transmissive electroconductive
member 20 (20A, 20B) having the elastomer layer 30 and the
electroconductive layer 25 (25A, 25B) formed thereon is superposed
in positional alignment with the LED chip, followed by vacuum hot
pressing, to provide a light-emitting device having introduced the
bump electrodes 36A and 36B (or 36).
[0168] With respect to the light-emitting device shown in FIG. 17
for example, the bump electrodes 36A and 36B, thus introduced, are
arranged in relative positions with the pad electrodes 15A and 15B
and the electroconductive layers 25A and 25B, e.g. as shown in a
plan view of FIG. 20.
<Production Process>
[0169] With reference to FIG. 16, the production process of the
light-emitting device 1A is explained.
[0170] The light-emitting device 1A having a partial sectional
structure schematically shown in FIG. 14, like the light-emitting
device 1 shown in FIG. 1 as the first embodiment, is formed through
a process of disposing the light-transmissive elastomer sheet 35
between the electrode layer 15 of the LED chip 10A and the
light-transmissive electroconductive layer 25 of the
light-transmissive electroconductive member 20; and subjecting the
resultant laminate to vacuum hot pressing at a temperature in a
range between 10.degree. C. below and 30.degree. C. higher than the
Vicat softening temperature of the light-transmissive elastomer,
thereby joining the LED chip 10A, the light-transmissive
electroconductive member 20 and the light-transmissive and
insulating substrate 21D, with the above-mentioned
light-transmissive elastomer.
[0171] As different from the first embodiment, it is sufficient to
dispose the light-transmissive elastomer sheet 35 at least between
the light-transmissive electroconductive layers 25C and the
electrode face of the LED chip and it is not necessary to always
insert a light-transmissive elastomer sheet between the transparent
substrate 21D and the LED chip. Accordingly, further explanation of
a production process is omitted.
[0172] According to the scanning electron microscope photograph,
the elemental mapping photograph of C by EDX and the elemental
mapping photograph of tin by EDC of the surfaces of the electrode
layer 15A and 15B after peeling at the boundary between the
electrode layers 15A and 15B of the LED chip 10, and the
light-transmissive electroconductive members 20C, the surfaces
exhibited almost identical states as the surface of the electrode
layer 15B in the first embodiment. Especially, both surfaces of the
electrode layers 15A and 15B of the LED 10 after peeling between
the electrode layers 15A and 15B and the light-transmissive
electroconductive member 20C, exhibited much C element and almost
no tin element near the surface centers thereof, and conversely,
much tin element and almost no C element near the edges of the
electrode layers 15 of the LED 10.
[0173] These results show that the electrode layer 15 and the
light-transmissive electroconductive layer 25 of the LED chip 10A
were in a good electrical connection.
[0174] Moreover, by existence of the region where a lot of C was
present with almost no tin on the surface of the electrode layer 15
of the LED 10, it was shown that there was a region where the
light-transmissive elastomer layer 30 entered between the electrode
layer 15 of the LED chip 10 and the light-transmissive
electroconductive layer 25 to mechanically join the electrode layer
15 of the LED chip 10 and the light-transmissive electroconductive
layers 25. Thus, it was understood that good electrical connection
and mechanical junction were satisfactorily maintained between the
electrode layer 15 of the LED chip 10A and the light-transmissive
electroconductive layer 25, also in the light-emitting device of
the second embodiment of the present invention.
[0175] Also in the second embodiment of the light-emitting device
of the present invention, good electric connection and mechanical
junction are realized between the electrode layer 15 of the LED
chip 10, and the light-transmissive electroconductive member 20 in
case where the elastomer coverage of the LED electrode 15A and the
LED electrode 15B is, 10% to 90%, more preferably 20% to 80%.
[0176] In the second embodiment of the present invention, the
production is performed by using an LED 10A on only one face of
which the electrode layers 15 (15A, 15B) are formed, the positional
alignment between the electrode layers 15 of the LED chip 10A and
the light-transmissive electroconductive layers 25 of the
light-transmissive electroconductive member 20C is required only
one side thereof. For this reason, production is easy and the yield
of the light-emitting device 1 becomes high.
[0177] By the way, although the above-mentioned embodiments have
been illustrated and explained mainly with respect to devices
containing one LED chip 10. However, the light-emitting device of
the present invention may include a plurality of LED chips 10, and
it is rather usual that more than two LED chips 10 are included and
arranged according to a desired display pattern.
[0178] Moreover, the light-emitting device can include one or more
types of semiconductor devices chosen from resistances, diodes,
transistors and ICs in addition to the LED chip(s) 10, on the
surface(s) of the light-transmissive electroconductive layer(s) 25
of the light-transmissive electroconductive member(s) 20.
<Comparison Between the Light-Emitting Device of the Present
Invention and the Conventional Light-Emitting Device>
[0179] When the conventional light-emitting device was reexamined
during a course of study up to completion of the present invention,
the following fact has become clear.
[0180] More specifically, it has been found that an edge of an
electrode on the surface of a light-emitting element is usually
formed so as to provide an almost right angle between its surface
opposite to the light-transmissive electroconductive layer of a
light-transmissive electroconductive member and its side wall, so
that at the time of bending of a light-emitting device or
application of a thermal cycle to a light-emitting device, the
light-transmissive electroconductive layer of the
light-transmissive electroconductive member is pressed and abutted
against the edge of the electrode of the surface of the
light-emitting element, thus being liable to produce a crack and a
breakage. When the crack or breakage occurs in the
light-transmissive electroconductive layer, electric connection of
a light-transmissive electroconductive layer becomes insufficient,
and a light-emitting device causes a lighting failure. This problem
occurs not only in production but also in use accompanied with
bending or application of thermal cycle to the light-emitting
device. Incidentally, the abutment of the light-transmissive
electroconductive layer at the time of application of thermal cycle
to a light-emitting device is caused by a difference in coefficient
of thermal expansion between component materials.
[0181] Moreover, a commercially available two-face electrode-type
LED is usually provided with an unevenness on the substrate face
and accordingly on the surface of the electrode so as to improve
the adhesiveness with an electric conduction paste in expectation
that the electrode on the non-light-emitting face is joined to a
lead frame with the electric conduction paste. Moreover, an
electrode surface on a luminescence face may be provided with fine
unevenness for preventing total reflection etc. In such a case, if
the light-transmissive electroconductive layer of the
light-transmissive electroconductive member is abutted to
convexities of such unevenness at the time of bending and
application of thermal cycle to the light-emitting device, a crack
or breakage is liable to occur in the light-transmissive
electroconductive layer. When the crack or breakage occurs in the
light-transmissive electroconductive layer, electric connection of
a light-transmissive electroconductive layer becomes insufficient,
and a light-emitting device causes a lighting failure.
[0182] Furthermore, in the light-emitting device disclosed in
Patent document 5, the thickness of an intermediate layer is
smaller than the thickness of a light-emitting element. As a
result, the light-transmissive electroconductive layer of the
light-transmissive electroconductive member is abutted strongly
against the surface edges of the electrode of the light-emitting
element at the time of bending of or application of thermal cycle
to the light-emitting device and is liable to cause crack or
breakage at the abutted parts. If the crack or breakage occurs in
the light-transmissive electroconductive layer, electric connection
of the light-transmissive electroconductive layer becomes
insufficient, and the light-emitting device causes a lighting
failure.
[0183] Thus, it was found that the conventional light-emitting
devices involved a problem that the light-transmissive
electroconductive layer of a light-transmissive electroconductive
member was liable to cause a crack or breakage at the time of
bending and application of thermal cycle and during production. If
the crack or breakage occurs in the light-transmissive
electroconductive layer, electric connection of a
light-transmissive electroconductive layer becomes insufficient,
and a light-emitting device causes a lighting failure.
[0184] Moreover, for production of conventional light-emitting
devices, thermal compression bonding has been performed under
atmospheric pressure, so that air bubbles (at a pressure higher
than atmospheric pressure) are liable to remain especially around
the LED chip in the light-emitting device. For this reason, it has
been found that the bubbles swell after the thermal compression
bonding to cause poor electric connection and undesirable
appearance due to irregular light scattering, etc. due to air
bubbles and swelling.
[0185] In the light-emitting device disclosed in Patent documents 4
and 5, since the light-transmissive electroconductive layer and the
LED electrode are merely physically in contact with each other and
with no material having a bonding function therebetween, it has
been found impossible to maintain a contact between the
light-transmissive electroconductive layer and the LED, when the
light-emitting device is bent in curvature radius of less than
about 100 mm, and a lighting failure occurs in less than several
hundreds of thermal cycles between high and low temperatures.
[0186] In the process disclosed in Patent document 3 of performing
heat-press bonding of a light-emitting element electrode and a
light-transmissive electroconductive layer, after inserting
therebetween an electrically insulating adhesive, such as a
flexible hot melt adhesion sheet, the hot melt adhesive is
heat-melted to be fluidized, intimately contacts the electrodes and
the electroconductive layer and solidifies on cooling to exhibit
the bonding ability, whereby electric and mechanical contacts
between the light-emitting element electrode and the
light-transmissive electroconductive layer, can be attained. The
hot melt adhesive is, however, melted and pressed for welding, as
is clearly described in Patent document 3. As a result, under
application of a pressure during production, the light-transmissive
electroconductive layer of a light-transmissive electroconductive
member is abutted against the edge of an electrode, the surface
unevenness of the electrode and a stepwise difference between the
substrate of a light-emitting element and the edge of an active
layer, etc., so that the light-transmissive electroconductive layer
is liable to cause a crack or a breakage which is however not
prevented by a hot melt adhesive as described above. Accordingly,
it becomes impossible to maintain a lighting state when it is
subjected to a thermal cycling test in temperature range of, e.g.
-20 to 60.degree. C., or -40.degree. C. to 85.degree. C. usually
required of electric parts, or when it is severely bent. In the
case of bonding an electrode and an electric conduction circuit
layer of an LED chip with an electrically conductive adhesive, it
is very difficult to achieve a sufficient insulation between a
plurality of LED chips carried and, in order to solve this, there
arises a manufacturing cost increase due to complication of a
connection step and an increase of involved steps, etc. Moreover,
when a conductive adhesive is used, it is difficult to ensure a
flexural resistance of the light-emitting device. Furthermore, it
has been found that since a hot melt adhesive is melted on heating,
it is difficult to perform an adhesion step under vacuum, and there
arises a vacant gap (air bubbles) with the residual air in the
light-emitting device, to result in poor connection and
appearance.
[0187] Based on the above-mentioned knowledge, the present
invention has been completed in order to solve the problems of the
conventional technology.
[Apparatus Including the Light-Emitting Device]
[0188] The apparatus of the present invention is equipped with the
above-mentioned light-emitting device of the present invention.
[0189] Examples of such apparatus suitably equipped with the
above-mentioned light-emitting device of the present invention, may
include: electronic appliances, such as a television set and a
personal computer; electronic display apparatus, such as an
exhibition plate and a bulletin board; movable bodies, such as
vehicles, a vessel and an airplane, equipped with illumination
apparatus or display apparatus including a light-emitting device; a
building, works, etc. equipped with illumination apparatus or
display apparatus including a light-emitting device.
EXAMPLES
[0190] Examples are shown below, whereas the present invention
should not be construed as being restricted thereto. Characteristic
values and evaluation thereof described in the present
specification including the following description are based on
methods and standards described below.
<Electrode Surface Roughness Ra>
[0191] Ra value was measured as an arithmetic average roughness
value measured according to JIS B 0601-2001 with respect to a
region of 1/3 or more of the crossing length of an objective
electrode.
<Sheet Resistivity of a Light-Transmissive Electroconductive
Layer>
[0192] Measured by the 4 terminal method based on JIS K 7194 for
any of the thin film-type electroconductive layer, the
electroconductive powder-dispersed resinous electroconductive layer
and the mesh electrode.
<Elastomer Properties>
[0193] The following properties were measured for the sheet-form
samples to be used. [0194] Vicat softening temperature was measured
according to the A50 method of the JIS K7206 (ISO 306) by using a
heat distortion tester No. 148-HD-PC (available from Yasuda Seiki
Seisakusho Ltd.) under the conditions of a test load of 10N and a
heating rate of 50.degree. C./hour. [0195] Glass transition
temperature and Melting temperature were measured by performing
heat flux differential scanning calorimetry according to JIS K2121
(ISO 3146), using Shimadzu differential scanning calorimeter DSC-60
at a heating rate of 5.degree. C./minute from -100.degree. C. to
the heat-absorption peak (melting point). [0196] Tensile storage
modulus was measured according to JIS K7244-4 (ISO 6721-4) using an
automatic dynamic viscoelasticity meter ("DDV-01GP", available from
A&D Co., Ltd.) under the conditions of a constant temperature
increase rate of 1.degree. C./minute and a frequency of 10 Hz.
Measurement was performed at 0.degree. C., 100.degree. C. and the
Vicat softening temperature.
[Characteristic Evaluation of Product Light-Emitting Device (LED
Device)]
[0197] The following items were evaluated.
<Thickness Between the LED Chips of a Light-Transmissive
Insulating Elastomer Layer>
[0198] A thickness of a light-transmissive insulating elastomer
layer (in a strip-shaped LED device sample with a length of about
90 mm (width: about 50 mm) including 6 LED chips (each having a
planar size of 0.3 mm.times.0.3 mm and a height of 175 .mu.m)
arranged in a straight line with a spacing of about 5 mm from each
other and connected in series prepared in, e.g. Examples and
Comparative Examples described hereafter) in a room at 20.degree.
C., was optically measured at a position 1500 .mu.m separated from
an end of an LED chip disposed near the center. An arithmetic
average of the measured values for 12 sample devices was taken.
<Flexural Resistance>
[0199] Flexural resistance test was performed with respect to six
of twelve obtained samples of LED devices under a temperature of
20.+-.2.degree. C., a relative humidity of 60 to 70%, and an
environment of normal pressure (86-106 kPa).
[0200] First, there were provided plural species of cylinders for
measurement having radius of 100 mm to 20 mm successively
decreasing at a decrement of 10 mm and respectively having a
section of a uniform diameter and of a perfect circle.
[0201] Next, each strip-shaped LED device was set so that its
longitudinal direction formed a right angle with the axis of a
measurement cylinder, and so that the back (opposite to the
light-emitting face) of an LED chip was disposed along the surface
of the measurement cylinder. Then, each LED device was turned on
and, in this state, bent at 180 degrees over the surface of the
measurement cylinder, to evaluate the lighting state was
maintained. This evaluation was performed sequentially from a
measurement cylinder with a larger radius to a measurement cylinder
with a smaller radius, to record two smallest flexural radiuses
including 20 mm (which is evaluated to represent a practically
excellent flexural resistance) or alternative smallest radiuses and
the number of sample devices having maintained their lighting
states at the radiuses.
<Thermal Cycling Test>
[0202] The other six obtained LED device samples was subjected to a
thermal cycling test according to JIS C60068-14.
[0203] More specifically, each strip-shaped LED device disposed in
a horizontal state and in a lighting state was subjected to a
thermal cycling test in a temperature range of -20.degree. C. to
60.degree. C. including 30 minutes each of standing at -20.degree.
C. and 60.degree. C. and intermediate temperature increase and
temperature decrease respectively at a rate of 3.degree. C./min.
(i.e. 1 cycle of 53.3 minutes), and the number of samples in six
samples having maintained the lighting state was recorded,
respectively after 2000 cycles, 2500 cycles and 3000 cycles.
(Lighting Conditions)
[0204] As for the lighting conditions for the LED device in the
above-mentioned flexural resistance and thermal cycling tests, a
predetermined direct-current voltage was continuously impressed
between both end terminals of each LED device so that a basically
fixed current of 6 mA was flowed through 6 LED chips connected in
series, and electricity supply conditions were changed as
follows.
[0205] ITO-dispersed resin film: [0206] 1 .mu.m in thickness:
Terminal voltage 25V, [0207] 3 .mu.m in thickness: Terminal voltage
20V,
[0208] ITO-sputtered film: Terminal voltage 30V,
[0209] Ag grain mesh electrode film: Terminal voltage 20V.
<Appearance and Sectional Observation>
[0210] Sampled devices after the preparation were left standing for
24 hours in an environment of temperature of 20.+-.2.degree. C.,
relative humidity of 60 to 70% and normal pressure (86-106
kPa).
(Observation of Appearance)
[0211] Visual examination by viewing with eyes was conducted with
respect to light-transmissive LED light-emitting devices before and
after the above-mentioned flexural resistance test and thermal
cycling test.
[0212] More specifically, the front and back surfaces of each
light-transmissive LED device was observed with eyes, and the
presence or absence of air bubbles was checked as a primary check.
Samples with which no bubbles were observed were judged as "no
bubbles" and the examination was terminated.
[0213] On the other hand, samples with which air bubbles were
observed by the primary check were subjected to photographing of
air bubbles using a microscope with a camera (magnification:
.times.50). Using the photographs, a maximum distance between
arbitrarily selected two points on the contour of an air bubble was
measured and determined as an outer diameter of the bubble. Whether
the thus-determined diameter of bubble was equal to or exceeded the
LED chip size or 500 .mu.m, was checked. Based on the above
examination, the evaluation was performed according to the
following standard.
[0214] A: Air bubbles were not recognized by the primary check by
viewing with eyes.
[0215] B: Although air bubbles were slightly recognized by viewing
with eyes, no air bubbles having an outer diameter equal to or
exceeding the LED chip size or 500 .mu.m was observed by checking
with a microphotograph.
[0216] C: The air bubbles were recognized by viewing with eyes and
exhibited an outer diameter equal to or exceeding the LED chip size
or 500 .mu.m by checking with a microphotograph.
(Sectional Observation)
[0217] Sectional observation was performed with respect to
light-transmissive LED devices before and after the above-mentioned
flexural resistance test and thermal cycling test. More
specifically, each light-transmissive stripe-shaped LED device was
embedded within a resin for sectional observation, and the
resultant sample was subjected to ion milling by an ion milling
apparatus ("E-3500", available from Hitachi Ltd.) to expose a
section perpendicular to the longitudinal direction of the
strip-shaped LED device and showing a central LED chip, which
section was then observed at a magnification of about 10,000 to
evaluate the degree of contact between the front and back
electrodes and the light-transmissive electroconductive layers
opposite to the electrodes and the degree of filling with the
elastomer on the electrodes and near the LED chip peripheral wall.
The evaluation was performed according to the following
standard.
[0218] A: Electrodes on an LED chip and the adjacent
electroconductive layers on the light-transmissive
electroconductive members exhibited a contact with each other, and
the elastomer filled up the crevice gap between the unevenness on
the electrodes and the opposite electroconductive layers. The
elastomer filled up to the peripheral wall of the LED chip.
[0219] A2: The electrodes on a one-face electrode-type LED chip and
the adjacent electroconductive layer on the light-transmissive
electro-conductive member exhibited a contact with each other, and
the elastomer filled up the crevice gap between the unevenness on
the above-mentioned electrode, and the electroconductive layer. The
elastomer filled up to the peripheral wall of the LED chip.
However, the elastomer did not fill the gap between the
electrode-free face of the LED chip and the adjacent transparent
substrate.
[0220] B1: The electroconductive layer and the adjacent
light-emitting side electrode of a two-face electrode-type LDE chip
exhibited a contact with each other, and the non-light-emitting
side electrode and the adjacent electroconductive layer exhibited a
contact with each other. And the circumference of the LED chip was
filled up with the elastomer. The crevice gap between the
unevenness on the non-light-emitting side electrode of the LED chip
and the adjacent electroconductive layer was filled up with the
elastomer. However, the crevice gap between the unevenness on the
light-emitting-side electrode of the LED chip and the adjacent
electroconductive layer was not filled with the elastomer.
[0221] C1: The electroconductive layer and the adjacent
light-emitting side electrode of a two-face electrode-type LDE chip
exhibited a contact with each other, and the non-light-emitting
side electrode and the adjacent electroconductive layer exhibited a
contact with each other. And the circumference of the LED chip was
filled up with the elastomer. The crevice gap between the
unevenness on the luminescent side electrode of the LED chip and
the adjacent electroconductive layer was filled up with the
elastomer. However, the crevice gap between the unevenness on the
nonlight-emitting-side electrode of the LED chip and the adjacent
electroconductive layers was not filled with the elastomer.
[0222] C2: The electrodes on a one-face electrode-type LED chip and
the electroconductive layers on the adjacent light-transmissive
electroconductive member contacted with each other in two pairs,
respectively, and the elastomer filled up to the peripheral wall of
the LED chip. However, the crevice gaps between the unevenness on
the above-mentioned electrodes and the adjacent electroconductive
layers, were not filled with the elastomer.
[0223] D: Although the electrodes on an LED chip and the adjacent
electroconductive layers on the light-transmissive
electro-conductive members exhibited a contact with each other, the
crevice gaps between the unevenness on the above-mentioned
electrodes and the adjacent electroconductive layers, were not
filled with the elastomer, and the elastomer did not fill up to the
peripheral wall of the LED chip.
<Elastomer Coverage of LED Electrode Surface>
(Two-Face Electrode-Type)
[0224] A light-transmissive LED device before and after the
above-mentioned flexural resistance test and thermal cycling test
and having an LED chip disposition similar to the one illustrated
in FIGS. 1 and 2 was subjected to a process including cutting-off
at a longitudinal end seal portion thereof with a diamond cutter,
and putting an about 5 mm-cut horizontally into the
light-transmissive elastomer layer 30 using a microtome. Square
bars made of stainless steel, having a width of 5 mm, thickness of
5 mm and a length identical to the end length of the
light-transmissive LED luminescent sheet (devices) and equipped
with a handle, was bonded firmly onto the outer surfaces at the cut
end of the light-transmissive electroconductive member 20A and 20B.
A double-face pressure sensitive adhesive tape having the same size
as the LED device sample was stuck on a horizontally disposed hard
plate, and the outer surface of the light-transmissive
electroconductive member 20B was stuck onto the double-face
adhesive tape to fix the LED device sample onto the hard plate.
While being maintained horizontally, the stainless steel bar bonded
to light-transmissive electroconductive member 20A was pulled up
slowly in a direction of 90 degrees to the light-transmissive
electroconductive member 20B, to peel the light-transmissive
electroconductive member 20A off the light-transmissive
electroconductive member 20B. As a result of repeating the above
operations, several LED device samples with exposed surface of
electrode 15A of the LED chip were prepared, and a part thereof was
used as a sample for elastomer coverage measurement of the
electrode layer 15A of the LED chip.
[0225] The remainder of the light-transmissive LED devices from
which the light-transmissive electroconductive member 20A had been
peeled, was subjected to application of a 180 .mu.m-thick PET film
with an adhesives onto the surface including the exposed electrode
15A, while being maintained horizontally, the stainless steel bar
bonded to the light-transmissive electroconductive member 20B as
mentioned above was pulled up slowly in a direction of 90 degrees
to a horizontal plane, to peel the LED device sample off the hard
plate. Next, the thus-peeled LED device sample was turned upside
down, and the outer surface of the applied 180 .mu.m-thick PET film
was stuck onto a hard plate via a double-face adhesive tape to fix
the LED device sample onto the hard plate. Then, while being
maintained horizontally, the stainless steel bar bonded to
light-transmissive electroconductive member 20B was pulled up
slowly in a direction of 90 degrees to the hard plate surface, to
peel the light-transmissive electroconductive member 20B off the
180 .mu.m-thick PET film applied with the adhesives. As a result,
the LED chip with the surface-exposed electrode 15B was left on the
PET film. This was used as a sample for elastomer coverage
measurement of the electrode layer 15B of the LED chip.
(One-Face Electrode-Type)
[0226] Light-transmissive one-face electrode-type LED devices
before and after the above-mentioned flexural resistance test and
thermal cycling test and having an LED chip disposition similar to
the one illustrated in FIG. 14 was treated in a similar manner as
the former half of the above section for two-face electrode-type
LED devices to peel only the light-transmissive electroconductive
member 20C and expose the face including the electrodes 15A and
15B, thereby making samples for measuring the elastomer coverages
of the electrodes.
[0227] The elastomer coverage measurement was performed by EDX
(energy dispersion-type X-ray analysis) using a "NORAY System SIX"
energy dispersion-type X-ray spectroscopic analyzer (made by Thermo
Fisher Scientific) attached to a field emission scanning electron
microscope ("ULTRA55", made by Carl Zeiss), including provision of
an electroconductive film of Pt--Pd on exposed electrode surfaces
of the above-prepared samples to effect elementary mapping. The
analysis was performed by using K-ray of carbon C to determine an
area (c) of carbon atom % of 50% or more and an area (d) of the
electrode per se and to calculate a ratio of c/d as an elastomer
coverage.
[Example 1] (Two-Face Electrode-Type LED Device)
[0228] A strip-shaped LED device having a general structure
including a length of about 90 mm and a width of about 50 mm was
prepared by disposing six two-face electrode-type LED chips
connected in series and arranged in a straight line with a spacing
of about 5 mm from each other and disposing a pair of elastomer
sheets respectively over the two faces of electrodes, followed by
sandwiching with a pair of light-transmissive electroconductive
member sheets and hot vacuum pressing. A partial laminate structure
thereof was similar as shown in FIGS. 1 and 2. Details thereof are
described below.
(LED Chip)
[0229] As LED chips, GaAlAs/GaAs-based red luminescence LED chips
(planar size: about 300.times.300 .mu.m, whole thickness (height):
175 .mu.m) having electrodes on both front and back faces, were
provided.
[0230] The electrode layers on both faces of each LED chip included
a substrate side electrode layer (15A) comprising a 3.5 .mu.m-thick
Au layer electrically connected to an N-type semiconductor
(N--GaAlAs) layer (42) of an LED body (11) via a semiconductor
substrate (41), and a light-emitting side electrode layer (15B)
comprising a 0.5 .mu.m-thick Au layer and electrically connected to
a P-type semiconductor (P--GaAlAs) layer (44) of the LED body. In
the LED chip, the substrate side electrode layer (15A) was formed
entirely on one face of the LED body (11), and the light-emitting
side electrode layer (15B) was formed on 20% of the other face of
the LED body.
[0231] In addition, in the LED chip, the substrate side electrode
layer (15A) had a surface roughness Ra of 0.5 .mu.m and the
light-emitting side electrode layer (15B) had a surface roughness
Ra of 0.13 .mu.m.
(Preparation of a Light-Transmissive Electroconductive Member)
[0232] Light-transmissive electroconductive members (20A, 20B) were
prepared. Each light-transmissive electroconductive member (20) was
formed by printing a slurry with ITO fine particles dispersed
therein on a 180 .mu.m-thick polyethylene terephthalate (PET) sheet
as a transparent substrate, followed by curing with ultraviolet
rays at room temperature to form a 1 .mu.m-thick electroconductive
layer and patterning thereof by laser irradiation, to form a
circuit layer (25) suitable for the series connection of six LED
chips arranged in a straight line as mentioned above. The slurry
comprised an ultraviolet-curable acrylic transparent resin in which
ITO particulates of 0.15 .mu.m in average particle size (aspect
ratio: 3.0) were dispersed at a rate of about 90 wt. %.
(Elastomer Sheet)
[0233] A 60 .mu.m-thick acrylic elastomer sheet having a Vicat
softening temperature of 110.degree. C. was provided as a material
constituting a light-transmissive elastomer layer (30), and cut
into a sheet (35) with an areal size almost the same as the
light-transmissive electroconductive member (20). The glass
transition temperature thereof was -40.degree. C., and the
elastomer exhibited a melting temperature of 220.degree. C., and
tensile storage moduli of 1.1 GPa at 0.degree. C., 0.3 GPa at
100.degree. C. and 0.2 GPa at 110.degree. C. (Vicat softening
temperature).
(Lamination)
[0234] With reference to FIG. 7 (however, used in a state of upside
down), first, a light-transmissive electroconductive member (20A)
was held so that its electric conduction circuitry layer was
directed upward. Then, an elastomer sheet (35) was laminated, and
also an LED chip (10) was disposed thereon, so that the
light-emitting side electrode layer (15B) was directed upward.
Next, another elastomer sheet (35) was laminated on the
light-emitting side electrode layer (15B) of the LED chip, and also
the light-transmissive electroconductive member (20B) was laminated
thereon with its electric conduction circuitry layer (25B) directed
downward.
(Preparation of a Light-Transmissive LED Luminescence Sheet)
[0235] The resultant laminate was subjected to a preliminary press
at a pressure of 0.1 MPa, a vacuum suction of the atmosphere to 5
or less kPa, and a vacuum hot pressing of 120.degree. C. and 10 MPa
for 10 minutes, thereby obtaining a light-transmissive LED
luminescence sheet (LED device) wherein the light-transmissive
elastomer layer (30) was densely formed between the
light-transmissive electroconductive members (20A-20B) and
surrounding the LED chip (10) without air bubbles. The peripheral
end faces of the obtained light-transmissive luminescence sheet
were sealed with a thermosetting resin, to obtain a strip-shaped
LED device.
[0236] The outline of the manufacturing conditions of
above-mentioned Example 1 is summarized and shown in Table 1
appearing hereinafter together with the results of the following
Examples and Comparative Examples.
[0237] The LED device obtained above was evaluated with respect to
the thickness of the light-transmissive insulating elastomer layer,
sectional observation, the elastomer coverage of the LED electrode,
the flexural resistance, and the thermal cycling test. The results
are summarized and shown in Table 2 appearing hereinafter together
with the results of the following Examples and Comparative
Examples.
[Example 2] (Two-Face Electrode-Type)
[0238] A light-transmissive LED device was prepared and evaluated
in the same manner as in Example 1 except that the thicknesses of
the electroconductive layers of the light-transmissive
electroconductive members both on the substrate side and the
light-emitting side were both changed to 2 .mu.m, the pressure and
heating temperature for the vacuum hot pressing of the laminate
were changed to 12 MPa and 110.degree. C., respectively.
[Example 3] (Two-Face Electrode-Type)
[0239] A light-transmissive LED device was prepared and evaluated
in the same manner as in Example 1 except that the thicknesses of
the electroconductive layers of the light-transmissive
electroconductive members both on the substrate side and the
light-emitting side were both changed to 3 .mu.m, the pressure and
heating temperature for the vacuum hot pressing of the laminate
were changed to 15 MPa and 100.degree. C., respectively.
[Example 4] (Two-Face Electrode-Type)
[0240] A light-transmissive LED device was prepared and evaluated
in the same manner as in Example 1 except that the thicknesses of
the electroconductive layers of the light-transmissive
electroconductive members both on the substrate side and the
light-emitting side were both changed to 3 .mu.m, and the elastomer
layer thickness was changed to 80 .mu.m.
<Sectional Observation>
[0241] In the light-transmissive LED luminescence sheets of the
above-described Examples, it was found that the electrode layers on
the substrate side and the light-emitting side on the front and
back faces of the LED chip exhibited a contact with the
electroconductive layers of the light-transmissive
electroconductive members on the substrate side and the
light-emitting side, respectively, the peripheral sides of the LED
chip were filled with the elastomer.
[0242] Further, in the light-transmissive LED luminescence sheets
of the above-described Examples, it was found that the crevice gap
between the surface unevenness on the substrate side electrode
layer of the LED chip and the electroconductive layer of the
light-transmissive electroconductive member on the substrate side
was filled up with the elastomer.
Comparative Example 1
(An Example Wherein an Elastomer Sheet was not Disposed on One of
Two-Face Electrodes)
[0243] A light-transmissive LED device was prepared and evaluated
in the same manner as in Example 1 except that the thicknesses of
the electroconductive layers (25A, 25B) of the light-transmissive
electroconductive members on the substrate side and the
light-emitting side were both changed to 3 .mu.m, no elastomer
sheet was disposed between the light-transmissive electroconductive
member (20A) and the substrate side electrode layer of the LED
chip, and a 120 .mu.m-thick elastomer sheet was disposed between
the light-transmissive electroconductive member (20B) on the
light-emitting side and the light-emitting side electrode layer
(15B) of the LED chip.
<Flexural Resistance Test>
[0244] In the light-transmissive LED luminescence sheet of this
experimental example, one of six samples caused a lighting failure
at a bending radius of 100 mm and all of the six samples caused a
lighting failure at a bending radius of 80 mm. After being released
from the bending, four samples recovered a lighting state. After 10
cycles of the flexural resistance test, all the six samples
remained in the non-lighting state even after being released from
the bending.
<Thermal Cycling Test>
[0245] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after
1500 cycles, and all six samples caused a lighting failure after
2000 cycles.
<Sectional Observation>
[0246] In the light-transmissive LED luminescence sheet of this
experimental example, the substrate side electrode layer and the
light-emitting side electrode layer on both faces of the LED chip
exhibited a contact with the electroconductive layer of the
light-transmissive electroconductive member on the substrate side
electrode layer and the electroconductive layer of the
light-transmissive electroconductive member on the light-emitting
side electrode layer, respectively, and the circumference of the
LED chip was filled up with the elastomer.
[0247] Further, in the light-transmissive LED luminescence sheet of
this experimental example, the crevice gap between the surface
unevenness on the light-emitting side electrode layer of the LED
chip and the electroconductive layer of the light-transmissive
electroconductive member on the light-emitting side electrode layer
in contact therewith was filled up with the elastomer.
[0248] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that the crevice gap
between the surface unevenness on the substrate side electrode
layer of the LED chip on which no elastomer layer was disposed at
the time of production, and the electroconductive layer of the
light-transmissive electroconductive member on the substrate side
electrode layer in contact therewith, was not filled with the
elastomer.
Example 5
(An Example of Disposing an Elastomer Sheet on the Electrode-Side
Face of a One-Face Electrode-Type LED Chip)
[0249] A strip-shaped LED device having a general structure roughly
identical to that of the device in Example 1 including a length of
about 90 mm and a width of about 50 mm was prepared by disposing,
however, one-face electrode-type LED chips connected in series and
arranged in a straight line with a spacing of about 5 mm from each
other and disposing an elastomer sheet over the electrodes on one
side, followed by sandwiching with a pair of light-transmissive
electroconductive member sheets and hot vacuum pressing. A partial
laminate structure thereof is similar as shown in FIGS. 14 and 15.
Details thereof are described below.
(LED Chip)
[0250] As LED chips, GaN-based blue luminescence LED chips (planar
size: about 350.times.350 .mu.m, whole thickness (height): 175
.mu.m) having two types of electrodes on one face thereof, were
provided. An LED chip (10A) had a structure including a
sapphire-made substrate (41A), and an N-type semiconductor layer
(42), a luminous layer (43) and a P-type semiconductor layer (44)
successively laminated in this order on the substrate. On one face
(light-emitting face) thereof on the side of the P-type
semiconductor layer (44), electrodes (15A and 15B) each comprising
1.5 .mu.m-thick Au were disposed so as to be electrically connected
with the N-type semiconductor layer (42) and the P-type
semiconductor layer (44), respectively. The electrodes 15A and 15B
each had a surface roughness Ra of 0.15 .mu.m.
(A Light-Transmissive Electroconductive Member and a Transparent
Substrate)
[0251] Similarly as in Example 1, a pair of transparent substrates
(21) each comprising a 180 .mu.m-thick polyethylene terephthalate
(PET) sheet, were provided, and one of these was made a
non-light-emitting-side transparent substrate 21D. On one surface
of the other transparent substrate 21C, a slurry obtained by
dispersing ITO particulates of 0.15 .mu.m in average particle size
(aspect ratio: 3) at a rate of about 90 wt. % in an
ultraviolet-curable acrylic transparent resin was applied and cured
with ultraviolet rays at room temperature to form a 3 .mu.m-thick
film. By partial removal (patterning) of the film by laser
irradiation, a light-transmissive electroconductive member 20C was
provided with an electroconductive layer 25A for connection with an
electrode 15A for an N-type semiconductor and an electroconductive
layer 25B for connection with electrode 15B for a P-type
semiconductor, which electroconductive layers 25A and 25B were
suitable for the series connection of six LED chips arranged in a
straight line, as mentioned above.
(Elastomer Sheet)
[0252] Similarly as in Example 1, a 60 .mu.m-thick elastomer sheet
having a Vicat softening temperature of 110.degree. C. was provided
and cut into an areal size comparable to that of the
light-transmissive electroconductive member 20C to provide an
elastomer sheet 35.
(Lamination)
[0253] With reference to FIG. 16, on an electroconductive layer
(25) directed upward of the light-transmissive electroconductive
member 20C, first an elastomer sheet 35 was laminated, the LED
chips 10A were disposed thereon so that light-emitting side
electrodes 15A and 15B were directed downward and positionally
aligned opposite to the electroconductive layers 25A and 25B,
respectively, of the light-transmissive electroconductive member
20C to be laminated with each other. Then, a transparent substrate
21 was laminated on the nonluminescent face 71 of the LED chips
10A, without disposing an elastomer sheet therebetween.
(Preparation of a Light-Transmissive LED Luminescence Sheet)
[0254] The resultant laminate was subjected to a preliminary press
at a pressure of 0.1 MPa, a vacuum suction of the atmosphere to 5
or less kPa, and a vacuum hot pressing of 120.degree. C. and 10 MPa
for 10 minutes, thereby obtaining a light-transmissive LED
luminescence sheet (LED luminescent device) wherein the
light-transmissive elastomer 30 filled between the
light-transmissive electroconductive member 20c with the
transparent substrate 21c and surrounding the LED chips 10A without
air bubbles, to provide a light-transmissive LED luminescence sheet
1A (FIG. 14). The peripheral end faces of the obtained
light-transmissive LED luminescence sheet were sealed with a
thermosetting resin, to obtain a strip-shaped LED luminescent
device, which was then evaluated in the same manner as in Example
1.
<Sectional Observation>
[0255] In the light-transmissive LED luminescence sheets of the
above-described Example, it was found that the two types of
light-emitting-side electrode layers formed on one face of the LED
chip exhibited a contact with the electroconductive layers of the
light-transmissive electroconductive member, and the peripheral
sides of the LED chip were filled with the elastomer.
[0256] Further, in the light-transmissive LED luminescence sheets
of the above-described Example, the crevice gaps between the
surface unevenness on the two types of light-emitting-side
electrode layers of the LED chip and the electroconductive layers
in contact therewith of the light-transmissive electroconductive
member on the substrate side were found to be filled up with the
elastomer.
[0257] The gap between the electrode-free face of the LED chip and
the transparent substrate was found to be not filled with the
elastomer.
Example 6
(An Example of Disposing an Elastomer Sheet on the Electrode Side
Face of a One-Face Electrode-Type LED Chip)
[0258] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 5 except that the
thickness of the elastomer sheet 35 was changed to 80 .mu.m.
Comparative Example 2
(An Example of not Disposing an Elastomer Sheet on the
Electrode-Side Face of a One-Face Electrode-Type LED Chip)
[0259] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 5 except that a 60
.mu.m-thick elastomer sheet 35 was disposed not on the
electrode-side face but on the substrate-side face of the LED chip
10A.
<Flexural Resistance Test>
[0260] In the light-transmissive LED luminescence sheet of this
experimental example, one of six samples caused a lighting failure
at a bending radius of 50 mm and all of the six samples caused a
lighting failure at a bending radius of 40 mm. After being released
from the bending, four samples recovered a lighting state. After 10
cycles of the flexural resistance test, all the six samples
remained in the non-lighting state even after being released from
the bending.
<Thermal Cycling Test>
[0261] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after
100 cycles, and all six samples caused a lighting failure after 500
cycles.
<Sectional Observation>
[0262] In the light-transmissive LED luminescence sheet of this
experimental example, the two types of the light-emitting side
electrode layers on one face of the LED chip exhibited a contact
with the electroconductive layers of the light-transmissive
electroconductive member, and the circumference of the LED chip was
filled up with the elastomer.
[0263] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that the crevice gaps
between the surface unevenness on the two types of the
light-emitting-side electrode layers of the LED chip and the
electroconductive layers in contact therewith of the
light-transmissive electroconductive member, were not filled with
the elastomer.
[0264] On the contrary, the gap between the electrode-free face of
the LED chip and the transparent substrate was filled up with the
elastomer.
Example 7
(An Example of Disposing an Elastomer Sheet on Both Faces of a
One-Face Electrode-Type LED Chip)
[0265] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 5 except that the
thickness of the elastomer sheet 35 was changed to 30 .mu.m, and
such a 30 .mu.m-thick elastomer sheet was disposed not only on the
two light-emitting-side electrode layers of the LED chip and also
between the other face of the LED chip and the transparent
substrate.
Example 8
(An Example Wherein an Elastomer Sheet was Disposed on Both Faces
of a Two-Face Electrode-Type LED Chip and the Electroconductive
Layer was Formed by Sputtering)
[0266] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 1 except for using a
light-transmissive electroconductive member obtained by forming not
a coated-and-cured slurry type electroconductive layer but a 0.15
.mu.m-thick ITO sputtered film as an electroconductive layer on the
180 .mu.m-thick PET sheet.
Example 9
[0267] (An Example Wherein an Elastomer Sheet was Disposed on Both
Faces of a Two-Face Electrode-Type LED Chip and the
Electroconductive Layers were Formed by Sputtering)
[0268] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 8 except that a 45
.mu.m-thick elastomer sheet having a Vicat softening temperature of
140.degree. C. was used, and the vacuum hot pressing was performed
at 140.degree. C.
Comparative Example 3
[0269] (An Example Wherein an Elastomer Sheet was Disposed on One
Face of a Two-Face Electrode-Type LED Chip and the
Electroconductive Layers were Formed by Sputtering)
[0270] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 8 except that
light-transmissive electroconductive members were prepared by
forming electroconductive layers by sputtering similarly as in
Example 8, and a 100 .mu.m-thick elastomer sheet was disposed only
on the light-emitting-side face and not on the non-light-emitting
side face of the LED chip.
<Flexural Resistance Test>
[0271] In the light-transmissive LED luminescence sheet of this
experimental example, one of six samples caused a lighting failure
at a bending radius of 100 mm and all of the six samples caused a
lighting failure at a bending radius of 80 mm. After being released
from the bending, four samples recovered a lighting state. After 10
cycles of the flexural resistance test, all the six samples
remained in the non-lighting state even after being released from
the bending.
<Thermal Cycling Test>
[0272] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after 50
cycles, and all six samples caused a lighting failure after 500
cycles.
<Sectional Observation>
[0273] In the light-transmissive LED luminescence sheet of this
experimental example, the two types of electrode layers on both
faces of the LED chip exhibited a contact with the
electroconductive layers of the light-transmissive
electroconductive members, and the circumference of the LED chip
was filled up with the elastomer.
[0274] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that the crevice gap
between the surface unevenness on the nonlight-emitting-side
electrode layer of the LED chip and the electroconductive layer in
contact therewith of the light-transmissive electroconductive
member was not filled with the elastomer.
[0275] On the other hand, the gap between the luminescence face of
the LED chip and the transparent substrate was filled up with the
elastomer.
Example 10
[0276] (An Example Wherein an Elastomer Sheet was Disposed on Both
Faces of a One-Face Electrode-Type LED Chip and the
Electroconductive Layers were Formed by Sputtering)
[0277] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 7 except that a
light-transmissive electroconductive member was prepared by forming
electroconductive layers by sputtering similarly as in Example
8.
Comparative Example 4
[0278] (An Example Wherein an Elastomer Sheet was not Disposed on
the Electrode Face of a One-Face Electrode-Type LED Chip and the
Electroconductive Layers were Formed by Sputtering)
[0279] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Comparative Example 2 except
that a light-transmissive electroconductive member was prepared by
forming electroconductive layers by sputtering similarly as in
Example 8.
<Flexural Resistance Test>
[0280] In the light-transmissive LED luminescence sheet of this
experimental example, two of six samples caused a lighting failure
at a bending radius of 50 mm and all of the six samples caused a
lighting failure at a bending radius of 40 mm. Even after being
released from the bending, 5 samples did not recover a lighting
state.
<Thermal Cycling Test>
[0281] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after
100 cycles, and all six samples caused a lighting failure after 500
cycles.
Example 11
[0282] (An Example Wherein an Elastomer Sheet was Disposed on the
Electrode Face of a One-Face Electrode-Type LED Chip and the
Electroconductive Layers were Formed by Sputtering)
[0283] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 5 except that a
light-transmissive electroconductive member was prepared by forming
electroconductive layers by sputtering similarly as in Example
8.
Examples 12, 15 and 16
[0284] Light-transmissive LED luminescent devices were prepared and
evaluated in the same manner as in Example 5 except that the
thicknesses of the electroconductive layers of light-transmissive
electroconductive members were changed to 5 .mu.m, 0.5 .mu.m and 12
.mu.m, respectively.
[0285] In the flexural resistance test, the light-transmissive LED
luminescence sheets of all these Examples exhibited a result that
all the six samples retained the lighting state of the LED chips at
bending radii down to 30 mm.
[0286] In the thermal cycling test, the light-transmissive LED
luminescence sheets of all these Examples exhibited a result that
all the six samples retained the lighting state of the LED chips
even after 2500 cycles.
Examples 13 and 14
[0287] Light-transmissive LED luminescent devices were prepared and
evaluated in the same manner as in Example 1 except that the
thicknesses of the electroconductive layers were changed to 0.5
.mu.m and 12 .mu.m, respectively.
Example 17
[0288] Silver halide as a photosensitive compound was applied on a
180 .mu.m-thick PET sheet, exposed and developed to provide a
light-transmissive electroconductive member having a square
lattice-shaped Ag particle mesh electrode layer with a thickness of
1 .mu.m, a line diameter of 10 .mu.m and an opening of 500 .mu.m as
a light-transmissive electroconductive layer.
[0289] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 1 except for using the
light-transmissive electroconductive member instead of the
light-transmissive electroconductive member having an ITO-dispersed
and cured resin film-type light-transmissive electroconductive
layer.
Example 18
[0290] A light-transmissive LED luminescent device was prepared and
evaluated in the same manner as in Example 5 except for using the
light-transmissive electroconductive member used in Example 17
instead of the light-transmissive electroconductive member having
an ITO-dispersed and cured resin film-type light-transmissive
electroconductive layer.
Comparative Example 5
[0291] (An Example Wherein Two-Face Electrode-Type LED Chips were
Disposed in Through-Holes Provided in an Elastomer Sheet)
[0292] A light-transmissive LED luminescence sheet was prepared by
a process disclosed in Patent document 5.
(LED Chip)
[0293] Elastomer sheets having a Vicat softening temperature of
110.degree. C. similarly as those used in Example 1 but having a
thickness of 120 .mu.m were used to form strip-shaped elastomer
sheets with a planar shape identical to those used in Example 1,
which were then bored to form six through-holes each suitable for
accommodating six LED chips therein. Elastomer sheets thus formed
were disposed to accommodate six LED chips disposed in series
within the through-holes, and were thereafter subjected to hot
vacuum pressing to prepare a light-transmissive LED luminescence
sheet, similarly as in Example 1.
<Flexural Resistance Test>
[0294] In the light-transmissive LED luminescence sheet of this
experimental example, all six samples caused a lighting failure at
bending radii down to 100 mm.
<Thermal Cycling Test>
[0295] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after
500 cycles, and all six samples caused a lighting failure after 550
cycles.
<Sectional Observation>
[0296] In the light-transmissive LED luminescence sheet of this
experimental example, the substrate-side electrode layer and the
light-emitting side electrode layer on both faces of the LED chip
exhibited a contact with the electroconductive layers of the
light-transmissive electroconductive members on the substrate side
and the light-emitting side, and the circumference of the LED chip
was filled up with the elastomer.
[0297] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that neither the crevice
gap between the surface unevenness on the substrate-side electrode
layer of the LED chip and the electroconductive layer in contact
therewith of the light-transmissive electroconductive member, nor
the crevice gap between the surface unevenness on the
light-emitting-side electrode layer of the LED chip and the
electroconductive layer in contact therewith of the
light-transmissive electroconductive member, was filled with the
elastomer.
Comparative Example 6
[0298] (An Example Wherein the Circumference of a One-Face
Electrode-Type LED Chip was Filled Up with an Adhesive)
[0299] A light-transmissive LED luminescence sheet was produced by
a process disclosed in Patent document 4.
(LED Chip)
[0300] LED chips, a strip-shaped light-transmissive
electroconductive member and a strip-shaped transparent substrate,
all identical to those used in Example 5, were used.
(Lamination)
[0301] Description is made by using reference symbols shown in FIG.
16. A light-transmissive electroconductive member 20C was held so
that electroconductive layers 25A and 25B were directed upward, and
thereon, the LED chips 10A were disposed so that their two types of
electrode layers 15A and 15B as luminescence-side electrode layers
were directed downward and aligned with electroconductive layers
25A and 25B, respectively, and fixed with each other with an
anisotropic electroconductive adhesive. Then, a transparent
substrate 21D was laminated over electrode-free upper faces of the
LED chips 10A.
(Production of a Light-Transmissive LED Luminescence Sheet)
[0302] The resultant laminate was placed under a vacuum of 5 kPa or
below, and an ultraviolet-curable acrylic resin-based adhesive was
injected between the light-transmissive electroconductive member
20C and the transparent substrate 21D, and around the LED chips
10A, so as not to leave gaps. Then, the ultraviolet-curable acrylic
resin-based adhesive was partially cured by irradiation with
ultraviolet rays.
[0303] As a result, there was obtained a light-transmissive LED
luminescence sheet, as a luminescent device having a flexural
resistance and including the surfaces of the LED chip 10A, other
than electrode layers 15A and 15B, bonded with the
light-transmissive electroconductive member and the transparent
substrate. The end faces of the light-transmissive LED luminescence
sheet were sealed with a thermosetting resin, to obtain a strip
shaped LED luminescent device, which was then evaluated in the same
manner as in Example 5.
<Flexural Resistance Test>
[0304] In the light-transmissive LED luminescence sheet of this
experimental example, all six samples caused a lighting failure at
bending radii down to 60 mm.
<Thermal Cycling Test>
[0305] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after 60
cycles, and all six samples caused a lighting failure after 600
cycles.
<Sectional Observation>
[0306] In the light-transmissive LED luminescence sheet of this
experimental example, the two types of the light-emitting side
electrode layers on one face of the LED chip exhibited a contact
with the electroconductive layers of the light-transmissive
electroconductive member, and the circumference of the LED chip was
filled up with the elastomer.
[0307] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that neither the crevice
gap between the surface unevenness on the substrate-side electrode
layer of the LED chip and the electroconductive layer in contact
therewith of the light-transmissive electroconductive member, nor
the crevice gap between the surface unevenness on the
light-emitting-side electrode layer of the LED chip and the
electroconductive layer in contact therewith of the
light-transmissive electroconductive member, was filled with the
acrylic resin-based adhesive.
Comparative Example 7
(An Example Wherein a Hot Melt Adhesive Sheet was Disposed Over
Both Faces of Two-Face Electrode-Type LED Chips)
[0308] A strip-shaped LED luminescent device was prepared and
evaluated in the same manner as in Example 1 except for disposing a
commercially available 60 .mu.m-thick hot melt adhesive sheet
having a softening temperature of 120.degree. C. as measured by a
ring and ball method (JIS K7234), instead of the elastomer sheet,
over both faces of the LED chips to form a laminate; and subjecting
the laminate to 1 minute of pressing at a pressure of 100
kgf/cm.sup.2 in an environment of atmospheric pressure and a
temperature of 180.degree. C., to provide a light-transmissive LED
luminescent sheet.
<Flexural Resistance Test>
[0309] In the light-transmissive LED luminescence sheet of this
comparative example, all six samples retained a lighting state down
to a bending radius of 60 mm but caused a lighting failure at a
bending radius of 30 mm.
<Thermal Cycling Test>
[0310] In the light-transmissive LED luminescence sheet of this
experimental example, all six samples caused a lighting failure
after 600 cycles.
<Sectional Observation>
[0311] In the light-transmissive LED luminescence sheet of this
comparative example, almost no adhesive was found to be present in
the crevice gap between the surface unevenness on the
substrate-side electrode layer of the LED chip and the
electroconductive layer in contact therewith of the
light-transmissive electroconductive member, or the crevice gap
between the surface unevenness on the light-emitting-side electrode
layer of the LED chip and the electroconductive layer in contact
therewith of the light-transmissive electroconductive member.
Comparative Example 8
[0312] With reference to FIG. 9, a light-transmissive LED
luminescent sheet was prepared and evaluated in the same manner as
in Example 1 except for changing both the thickness of the
electroconductive layer (25A) of the light-transmissive
electroconductive member on the substrate-side electrode layer and
the thickness of the electroconductive layer (25B) of the
light-transmissive electroconductive member on the
light-emitting-side electrode layer to 3 .mu.m, omitting the
disposition of an elastomer sheet between the light-transmissive
electroconductive member on the light-emitting surface and the
light-emitting surface-side electrode layer (15B) of the LED chip,
and changing the thickness of the elastomer sheet (35) disposed
between the light-transmissive electroconductive member (25A) on
the substrate-side electrode layer and the substrate-side electrode
layer (15A) of the LED chip to 120 .mu.m.
<Flexural Resistance Test>
[0313] In the light-transmissive LED luminescence sheet of this
experimental example, one of six samples caused a lighting failure
at a bending radius of 100 mm and all of the six samples caused a
lighting failure at a bending radius of 80 mm. After being released
from the bending, four samples recovered a lighting state. After 10
cycles of the flexural resistance test, all the six samples
remained in the non-lighting state even after being released from
the bending.
<Thermal Cycling Test>
[0314] In the light-transmissive LED luminescence sheet of this
experimental example, one sample caused a lighting failure after
1500 cycles, and all six samples caused a lighting failure after
2000 cycles.
<Sectional Observation>
[0315] In the light-transmissive LED luminescence sheet of this
experimental example, the substrate side electrode layer and the
light-emitting side electrode layer on both faces of the LED chip
exhibited a contact with the electroconductive layer of the
light-transmissive electroconductive member on the substrate side
electrode layer and the electroconductive layer of the
light-transmissive electroconductive member on the light-emitting
side electrode layer, respectively, and the circumference of the
LED chip was filled up with the elastomer.
[0316] Further, in the light-transmissive LED luminescence sheet of
this experimental example, the crevice gap between the surface
unevenness on the light-emitting side electrode layer of the LED
chip and the electroconductive layer of the light-transmissive
electroconductive member on the side of the light-emitting side
electrode layer in contact therewith was filled up with the
elastomer.
[0317] However, in the light-transmissive LED luminescence sheet of
this experimental example, it was found that the crevice gap
between the surface unevenness on the substrate side electrode
layer of the LED chip on which no elastomer layer was disposed at
the time of production, and the electroconductive layer of the
light-transmissive electroconductive member on the substrate side
electrode layer in contact therewith, was not filled with the
elastomer.
[0318] With respect to the above-mentioned Examples and Comparative
Examples, the outline of the production conditions are summarized
in Table 1 and the evaluation results are collectively shown in
Table 2, respectively.
TABLE-US-00001 TABLE 1 Disposed on lower Disposed on face (*1) of
LED. LED upper face (*2) of LED. Transmissive Elasto- Electrode
Elasto- Transmissive Property of conductive member mer Two mer
conductive member conductor member Conductive sheet elec Height
sheet Conductive Total Substrate layer (*3) trodes (.mu.m) (*4)
Whole (*3) Substrate layer Sheet light Thick- Thick- Thick- on one
Lower Upper thick- Thick- Thick- Thick- Conduc- Resis- trans- Exam-
ness ness ness or two face face ness ness ness ness tive tivity
mittance Haze ple (.mu.m) (.mu.m) (.mu.m) faces *1 *2 (.mu.m)
(.mu.m) (.mu.m) (.mu.m) layer (.OMEGA./.quadrature.) (%) (%) 1 180
1 60 two 0.5 3.5 175 60 180 1 ITO 180 86 1.2 faces dispersed 2 180
2 60 two 0.5 3.5 175 60 180 2 ITO 90 83 1.5 faces dispersed 3 180 3
60 two 0.5 3.5 175 60 180 3 ITO 40 83 1.5 faces dispersed 4 180 3
80 two 0.5 3.5 175 80 180 3 ITO 40 83 1.5 faces dispersed 5 180 3
60 one 1.5 -- 90 -- 180 -- ITO 40 83 1.5 face dispersed 6 180 3 80
one 1.5 -- 90 -- 180 -- ITO 40 83 1.5 face dispersed 7 180 1 30 one
1.5 -- 90 30 180 -- ITO 180 86 1.2 face dispersed 8 180 0.15 60 two
0.5 3.5 175 60 180 0.15 ITO 50 85 1.1 faces sputtered 9 180 0.15 45
two 0.5 3.5 175 45 180 0.15 ITO 50 85 1.1 faces sputtered 10 180
0.15 30 one 1.5 -- 90 30 180 -- ITO 50 85 1.1 face sputtered 11 180
0.15 60 one 1.5 -- 90 -- 180 -- ITO 50 85 1.1 face sputtered 12 180
5 60 one 1.5 -- 90 -- 180 -- ITO 30 75 2.5 face dispersed 13 180
0.5 60 two 0.5 3.5 175 60 180 0.5 ITO 1500 86 0.8 faces dispersed
14 180 12 60 two 0.5 3.5 175 60 180 12 ITO 30 48 10 faces dispersed
15 180 0.5 60 one 1.5 -- 90 -- 180 -- ITO 1500 86 0.8 face
dispersed 16 180 12 60 one 1.5 -- 90 -- 180 -- ITO 30 48 10 face
dispersed 17 180 1 60 two 0.5 3.5 175 60 180 1 Ag 10 82 2.5 faces
mesh 18 180 1 60 one 1.5 -- 90 -- 180 1 Ag 10 82 2.5 face mesh
Comp.1 180 3 120 two 0.5 3.5 175 -- 180 3 ITO 40 83 1.5 faces
dispersed Comp.2 180 3 -- one 1.5 -- 90 60 180 -- ITO 40 83 1.5
face dispersed Comp.3 180 0.15 100 two 0.5 3.5 175 -- 180 0.15 ITO
50 85 1.1 faces sputtered Comp.4 180 0.15 -- one 1.5 -- 90 60 180
-- ITO 50 85 1.1 face sputtered Comp.5 180 3 -- two 0.5 3.5 175 --
180 3 ITO 40 83 1.5 *6 faces dispersed Comp.6 180 3 -- one 1.5 --
90 -- 180 -- ITO 40 83 1.5 *7 face dispersed Comp.7 180 3 60*.sup.5
two 0.5 3.5 175 60*.sup.5 100 3 ITO 40 83 1.5 *8 faces dispersed
Comp.8 180 3 -- two 0.5 3.5 175 120 180 3 ITO 40 83 1.5 faces
dispersed *1: Disposed on a lower face in FIG. 2 (two-face
electrode-type LED), on a lower face in FIGS.15 and 16 (one-face
electrode-type LED). Light-emitting side in either case. *2:
Disposed on an upper face in FIG. 2 (two-face electrode-type LED),
on on an upper face in FIGS.15 and 16 (one-face electrode-type LED.
Non-light-emitting side in either case. *3: A light-transmissive
thermoplastic elastomer layer *4: Height above the LED chip body
*.sup.5Thickness (.mu.m) of a hot melt adhesive sheet *6: LED was
dispoded in a through-hole of an elastomer sheet. *7: Bonded with
an anisotropic conductive adhesive. *8: A hot melt adhesive sheet
was sandwiched between LED electrodes and opposite
electroconductive layers.
TABLE-US-00002 TABLE 2 Flexural resistance Number of lighting
samples Appearance & Number Number after thermal cycling test
Elastomer Sectional of of After After After Coverage observation
lighting Minimum lighting 2000 2500 3000 Total On Elec- On Elec-
Sectional Bending samples bending samples cycles sr cycles cycles
thickness trode 15A trode 15B Appear- Obser- Radius (piece/ radius
(piece/ (piece/ (piece/ (piece/ Example (.mu.m) (%) (%) ance vation
(mm) piece) (mm) piece) piece) piece) piece) 1 120 48 65 A A 30 6/6
20 6/6 6/6 6/6 6/6 2 120 35 56 A A 30 6/6 20 6/6 6/6 6/6 6/6 3 120
32 53 A A 30 6/6 20 6/6 6/6 6/6 6/6 4 160 67 80 A A -- -- 20 6/6 --
-- 6/6 5 60 62 74 A A 30 6/6 20 6/6 6/6 6/6 6/6 6 60 25 43 A A2 --
-- 20 6/6 -- -- 6/6 7 60 18 34 A A -- -- 20 6/6 -- -- 6/6 8 120 69
78 A A 40 6/6 20 4/6 6/6 4/6 3/6 9 90 54 64 B B1 40 6/6 20 3/6 6/6
-- 3/6 10 60 23 29 A A 40 6/6 20 3/6 6/6 -- 2/6 11 60 72 63 A A 40
6/6 30 5/8 6/6 5/6 2/6 12 60 62 74 A A 30 6/6 20 6/6 6/6 6/6 6/6 13
120 48 65 A A 30 6/6 20 4/6 6/6 6/6 4/6 14 120 48 65 A A 30 6/6 20
5/6 6/6 6/6 5/6 15 60 62 74 A A 30 6/6 20 5/6 6/6 4/6 4/6 16 60 62
74 A A 40 6/6 20 4/6 6/6 5/6 5/6 17 120 48 65 A A 30 6/6 20 6/6 6/6
6/6 6/6 18 60 62 74 A A 30 6/6 20 6/6 6/6 6/6 6/6 Comp.1 120 7 78 B
C1 100 5/6 80 0/6 0/6 -- -- Comp.2 60 2 4 B C2 50 5/6 40 0/6 0/6 --
-- Comp.3 100 3 67 C C1 100 5/6 80 0/6 0/6 -- -- Comp.4 60 3 5 C C2
50 4/6 40 0/6 0/6 -- -- Comp.5 120 2 3 C D -- -- 100 0/6 0/6 -- --
Comp.6 175*.sup.1 2 4 C D 60 0/6 -- -- -- -- Comp.7 120*.sup.2 12 9
C D 60 6/6 30 0/6 0/6 -- -- Comp.8 120 75 6 B B1 100 5/6 80 0/6 0/6
-- -- *.sup.1: Thickness (.mu.m) of adhesive layer *.sup.2:
Thickness (.mu.m) of hot melt adhesive layer
[0319] In the above, although some embodiments of the present
invention have been described, these embodiments are presented
merely as an example and are not intended to limit the scope of the
invention. These novel embodiments can be practiced in various
other forms and can be subjected to various omission, replacement
and modification. These embodiments and modifications thereof are
included in the scope and gist of the invention, and they are
included in the invention recited in the claims, and equivalents
thereof.
INDUSTRIAL APPLICABILITY
[0320] As mentioned above, the present invention provides a
light-emitting device which is excellent in flexural resistance and
thermal cycle characteristic and can maintain a lighting state in
resistance to strong bending and heat load, through a production
process characterized by vacuum pressing at a temperature around or
slightly above the Vicat softening temperature of a
light-transmissive elastomer.
DESCRIPTION OF NOTATIONS
[0321] 1, 1A, 1B, 90, 90A: Light-emitting device [0322] 10: LED
Chip (Two-face Electrode-type), 10A LED chip (One-face
Electrode-type) [0323] 11: LED body (Two-face Electrode-type), 11A
LED body (One-face Electrode-type) [0324] 13: Circumference of LED
Chip [0325] 15: Electrode Layer [0326] 15A: First electrode layer
(cathode layer, electrode layer) [0327] 15B: Second electrode layer
(anode layer, electrode layer) [0328] 17: Peripheral Face of
Electrode Layer [0329] 18: Edge of Electrode Layer [0330] 20:
Light-transmissive Electroconductive Member [0331] 20A: First
light-transmissive electroconductive member [0332] 20B: Second
light-transmissive electroconductive member [0333] 20C:
Light-transmissive electroconductive member of a second embodiment
[0334] 21, 21A, 21B, 21C, 21D: Transparent substrate [0335] 25:
Light-transmissive Electroconductive Layer [0336] 25A: First
light-transmissive electroconductive layer (light-transmissive
electroconductive layer) [0337] 25B: Second light-transmissive
electroconductive layer (light-transmissive electroconductive
layer) [0338] 26: Surface of Light-transmissive Electroconductive
Layer [0339] 30: Light-transmissive Elastomer Layer [0340] 35:
Temporary Light-transmissive-Elastomer Layer [0341] 36, 36A, 36B:
Bump electrode [0342] 36S: Au bump [0343] 41: LED Semiconductor
Substrate (Two-face Electrode-type) [0344] 41A: LED heat-resistant
board (One-face electrode-type) [0345] 42: N-type Semiconductor
Layer [0346] 44: P-type Semiconductor Layer [0347] 43: Luminescent
Layer [0348] 45: Unevenness [0349] 46: Concavity [0350] 47:
Convexity [0351] 48: Crevice gap [0352] 71: Face of LED Body [0353]
71A: First face of LED body [0354] 71B: Second face of LED body
[0355] 71C: Third face of LED body [0356] 71D: Fourth face of LED
body [0357] 72: N-type Semiconductor Luminescent Layer-side
Boundary [0358] 85: Light-emitting face [0359] 91: Opening [0360]
92: Crack [0361] 95: Fixing resin for sectional observations
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