U.S. patent application number 09/548273 was filed with the patent office on 2002-03-07 for method of and apparatus for bonding light-emitting element.
Invention is credited to Miura, Katsuhiro, Yamamoto, Kiyohumi.
Application Number | 20020027650 09/548273 |
Document ID | / |
Family ID | 14383672 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027650 |
Kind Code |
A1 |
Yamamoto, Kiyohumi ; et
al. |
March 7, 2002 |
METHOD OF AND APPARATUS FOR BONDING LIGHT-EMITTING ELEMENT
Abstract
A light-transmissive support disk supports a tube for attracting
an LED chip, and a light-transmissive electrically conductive film
is disposed on the support base. The LED chip is electrically
connected to a negative terminal of a DC power supply by the
light-transmissive electrically conductive film. An imaging unit is
disposed coaxially with the tube and has a CCD camera for capturing
an image of a light-emitting state of the LED chip via the support
disk and a cover member when the LED chip attracted by the tube
emits light. The light-emitting center of the LED chip can be
detected accurately, and bonded easily and highly accurately on a
board at a desired position thereon.
Inventors: |
Yamamoto, Kiyohumi;
(Minamiashigara-shi, JP) ; Miura, Katsuhiro;
(Mitaka-shi, JP) |
Correspondence
Address: |
Sughrue Mion Zinn Macpeak & Seas PLLC
2100 Pennsylvania Avenue N W
Washington
DC
20037-3202
US
|
Family ID: |
14383672 |
Appl. No.: |
09/548273 |
Filed: |
April 12, 2000 |
Current U.S.
Class: |
356/121 |
Current CPC
Class: |
H01L 21/67144 20130101;
H05K 2203/166 20130101; Y02P 70/613 20151101; Y02P 70/50 20151101;
H05K 2201/10106 20130101; H05K 1/0269 20130101; H01L 21/681
20130101; H05K 3/303 20130101 |
Class at
Publication: |
356/121 |
International
Class: |
G01J 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 1999 |
JP |
11-104553 |
Claims
What is claimed is:
1. A method of bonding a light-emitting element on a board at a
predetermined position thereon, comprising the steps of: holding
the light-emitting element with a holder separate from or integral
with a light-transmissive support member from a direction in which
the light-emitting element emits light; energizing the
light-emitting element to emit light; imaging a light-emitting
state of the light-emitting element via said light-transmissive
support member; recognizing a light-emitting center of the
light-emitting element based on the imaged light-emitting state;
and positioning and bonding the light-emitting element held by said
holder on the board at a bonding position thereon based on the
recognized light-emitting center.
2. A method according to claim 1, further comprising the steps of:
determining four sides of a light-emission image based on the
imaged light-emitting state; thereafter, determining points of
intersection of said four sides; and determining a light-emitting
center at a point of intersection of diagonal lines passing through
said points of intersection for thereby recognizing the
light-emitting center.
3. An apparatus for bonding a light-emitting element on a board at
a predetermined position thereon, comprising: a light-transmissive
support member having a holder, separate therefrom or integral
therewith, for holding the light-emitting element from a direction
in which the light-emitting element emits light; light-emitting
means for energizing the light-emitting element held by said holder
to emit light; imaging means for imaging a light-emitting state of
the light-emitting element via said light-transmissive support
member; and image processing means for recognizing a light-emitting
center of the light-emitting element based on the imaged
light-emitting state.
4. An apparatus according to claim 3, further comprising: a
light-transmissive cover member, said light-transmissive support
member and said light-transmissive cover member jointly defining a
suction chamber therebetween; and a negative pressure source
connected to said holder through said suction chamber.
5. An apparatus according to claim 4, wherein said holder comprises
an electrically conductive tube, said electrically conductive tube
having a joining member projecting through a through hole defined
in said light-transmissive support member into said suction
chamber, said joining member having an end fixed by an adhesive to
a surface of said light-transmissive support member which faces
said suction chamber.
6. An apparatus according to claim 5, wherein said light-emitting
means comprises a light-transmissive electrically conductive film
disposed on said surface of said light-transmissive support member
which faces said suction chamber, said joining member being fixed
to said light-transmissive electrically conductive film by an
electrically conductive adhesive.
7. An apparatus according to claim 5, wherein said light-emitting
means comprises an electrically conductive member connected to said
joining member.
8. An apparatus according to claim 5, wherein said electrically
conductive tube has a tapered portion which is progressively
smaller in diameter away from said light-transmissive support
member.
9. An apparatus according to claim 8, wherein said light-emitting
means comprises a light-transmissive electrically conductive film
disposed on said surface of said light-transmissive support member
which faces said suction chamber, said joining member being fixed
to said light-transmissive electrically conductive film by an
electrically conductive adhesive.
10. An apparatus according to claim 8, wherein said light-emitting
means comprises an electrically conductive member connected to said
joining member.
11. An apparatus according to claim 4, wherein said light-emitting
means comprises a light-transmissive electrically conductive film
disposed on a surface of said light-transmissive support member
which is opposite to said suction chamber, said holder comprising
said light-transmissive electrically conductive film.
12. An apparatus according to claim 3, further comprising: a
movable tube disposed coaxially with said imaging means, said
light-transmissive support member being mounted on said movable
tube; rotating means for rotating said movable tube; and moving
means for moving said movable tube toward and away from said
imaging means.
13. An apparatus according to claim 12, wherein said movable tube
is rotatably supported by an air bearing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of and an
apparatus for bonding a light-emitting element to a board at a
predetermined position thereon.
[0003] 2. Description of the Related Art
[0004] Generally, a linear array of light-emitting elements such as
laser diodes (LDs), light-emitting diodes (LEDs), or the like is
used as a light source for image reading and outputting (recording)
applications. For example, as shown in FIG. 19 of the accompanying
drawings, an LED array 1 comprises a plurality of LED chips
(light-emitting elements) 3 mounted on a board 2 at equally spaced
intervals and arranged in a linear pattern extending in one
direction. The LED chips 3 are bonded on the board 2 by silver
paste, with gold wires 4 extending from the respective LED chips
3.
[0005] The LED array 1 requires that the LED chips 3 be aligned
highly accurately on the board 2 such that the LED chips 3 have
respective light-emitting centers spaced at equal intervals. To
meet such a requirement, it is necessary to recognize the
light-emitting center of each LED chip 3 from the vertical
direction in which the LED chip 3 emits light. However, since the
LED chip 3 is a very small chip having dimensions of 0.3
mm.times.0.3 mm, when the LED chip 3 is attracted by a collet, the
LED chip 3 is concealed almost in its entirety by the collet.
Therefore, when the LED chip 3 is attracted by the collet, the
collet makes it difficult to confirm the light-emitting center of
the LED chip 3 or even the outer configuration of the LED chip
3.
[0006] Inasmuch as the LED chip 3 is a very small chip, it is not
easy to apply an alignment mark to the LED chip 3 and hence the LED
chip 3 cannot be bonded on the board 2 according to a normal
alignment process. If the LED chip 3 is bonded on the basis of the
recognized outer configuration thereof, then because the
light-emitting center of the LED chip 3 and the center of the outer
configuration thereof generally do not agree with each other, the
light-emitting centers of the LED chips 3 tend to be misaligned
with each other even when the LED chips 3 are positioned accurately
the basis of the recognized outer configuration thereof.
[0007] Japanese laid-open patent publication No. 7-43112 discloses
a method of detecting the light-emitting spot of a light-emitting
element and an apparatus for positioning such a light-emitting
element. According to the disclosed method and apparatus, when a
semiconductor device laser chip is attracted by an attraction
nozzle and delivered to a positioning location, a current is
supplied to energize the semiconductor device laser chip, and a CCD
camera positioned in facing relationship to a light-emitting area
of the semiconductor device laser chip detects light emitted from
the semiconductor device laser chip. An image generated by the CCD
camera based on the detected light is supplied to a controller,
which detects the position and orientation of the semiconductor
device laser chip based on the image, and controls the attraction
nozzle to correct the attitude of the semiconductor device laser
chip.
[0008] However, since the disclosed arrangement employs the
semiconductor device laser chip as a light-emitting element, it
cannot be applied to LED chips whose light-emitting areas have a
complex shape. Inasmuch as the semiconductor device laser chip has
a chip attraction surface and a light-emitting surface which are
different from each other, the light-emitting state of the
semiconductor device laser chip can easily be detected while the
semiconductor device laser chip is being attracted. However, it is
quite difficult to detect the light-emitting center of an LED chip
because the LED chip has a chip attraction surface and a
light-emitting surface which are oriented in the same direction.
Another problem is that when a probe is applied to the LED chip to
cause the LED chip to emit light, the probe conceals the
light-emitting area of the LED chip, making it difficult to detect
the light-emitting center of the LED chip.
SUMMARY OF THE INVENTION
[0009] It is a major object of the present invention to provide a
method of and an apparatus for bonding a light-emitting element by
reliably detecting the light-emitting center of the light-emitting
element and positioning the light-emitting element highly
accurately and easily on a board.
[0010] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which preferred embodiments of the present invention
are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of a bonding apparatus for
carrying out a method of bonding a light-emitting element according
to a first embodiment of the present invention;
[0012] FIG. 2 is a vertical cross-sectional view of a collet unit
of the bonding apparatus;
[0013] FIG. 3 is a perspective view of a support disk and a tubular
body incorporated in the collet unit;
[0014] FIG. 4 is a plan view of the support disk;
[0015] FIG. 5 is an enlarged fragmentary vertical cross-sectional
view of the support disk and the tubular body;
[0016] FIGS. 6 and 7 are a flowchart of an operation sequence of
the method of bonding a light-emitting element;
[0017] FIG. 8 is a view showing an image of an LED chip which is
captured by a CCD camera;
[0018] FIG. 9 is a front elevational view showing the manner in
which the LED chip is removed from a chip laying base of the
bonding apparatus;
[0019] FIG. 10 is a front elevational view showing the manner in
which the LED chip is placed on a light-emitting base of the
bonding apparatus;
[0020] FIG. 11 is an enlarged fragmentary vertical cross-sectional
view of the collet unit as it attracts the LED chip;
[0021] FIG. 12 is a diagram showing the manner in which the
light-emitting state of the LED chip is imaged for an image
processing process;
[0022] FIG. 13 is a diagram illustrative of the image processing
process;
[0023] FIG. 14 a diagram showing a positional deviation between the
light-emitting center of the LED chip and the center of the CCD
camera;
[0024] FIG. 15 is a front elevational view showing the manner in
which the LED chip is bonded on a board;
[0025] FIG. 16 is an enlarged fragmentary vertical cross-sectional
view of a collet unit of a bonding apparatus according to a second
embodiment of the present invention;
[0026] FIG. 17 is a plan view of a support disk of the collet unit
shown in FIG. 16;
[0027] FIG. 18 is an enlarged fragmentary vertical cross-sectional
view of a collet unit of a bonding apparatus according to a third
embodiment of the present invention; and
[0028] FIG. 19 is a perspective view of an ordinary LED array.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] FIG. 1 shows in perspective a bonding apparatus 10 for
carrying out a method of bonding a light-emitting element according
to a first embodiment of the present invention.
[0030] The bonding apparatus 10 generally comprises a chip laying
base 14 for holding LED chips 12 as light-emitting elements in a
two-dimensional pattern, a collet unit 16 for attracting and
holding an LED chip 12, a light-emitting base (light-emitting
means) 18 for energizing a light-emitting area of the LED chip 12
attracted and held by the collect unit 16, an imaging means 20 for
imaging a light-emitting state of the LED chip 12, and a bonding
base 24 for bonding the LED chip 12 on a board 22.
[0031] A displacement mechanism 36 is mounted on an upper surface
34 of a mount base 32 of the bonding apparatus 10. The displacement
mechanism 36 has a first movable stage 40 movable along a Y-axis of
an orthogonal coordinate system by a first motor 38 and a second
movable stage 44 movable along an X-axis of the orthogonal
coordinate system with respect to the first movable stage 40 by a
second motor 42.
[0032] The first movable stage 40 comprises a pair of guide rails
46a, 46b extending along the Y-axis and a ball screw 48 disposed
between guide rails 46a, 46b and extending along the Y-axis. The
first motor 38 has an output shaft coupled to an end of the ball
screw 48. The ball screw 48 is threaded through a nut (not shown)
fixed to a lower surface of a Y-axis movable table 50 that is
movably supported on the guide rails 46a, 46b.
[0033] The Y-axis movable table 50 is of an elongate shape along
the X-axis. The Y-axis movable table 50 supports thereon a pair of
guide rails 52a, 52b extending along the X-axis and a ball screw 54
disposed between guide rails 52a, 52b and extending along the
X-axis. The guide rails 52a, 52b and the ball screw 54 belong to
the second movable stage 44. The second motor 42 has an output
shaft coupled to an end of the ball screw 54. The ball screw 54 is
threaded through a nut (not shown) fixed to a lower surface of an
X-axis movable table 56 that is movably supported on the guide
rails 52a, 52b.
[0034] The X-axis movable table 56 supports on an upper surface 58
thereof the chip laying base 14, the light-emitting base 18, and
the bonding base 24. The light-emitting base 18 is electrically
connected to the positive terminal (positive pole) of a DC power
supply (not shown).
[0035] A column 60 is vertically mounted on an end of the mount
base 32, and a third movable stage 62 for moving the collet unit 16
vertically along a Z-axis of the orthogonal coordinate system is
supported on the column 60. The third movable stage 62 has a frame
64 fixed to a vertical surface of the column 60, a third motor 66
fixedly mounted on an upper end of the frame 64, and a ball screw
68 connected to the output shaft of the third motor 66 and
extending along the Z-axis and threaded through a vertically
movable base 70 guided by the frame 64.
[0036] The collet unit 16 has a casing 72 fixed to the vertically
movable base 70. As shown in FIG. 2, the imaging means 20 has a CCD
camera 74 mounted on an upper end of the casing 72 and a magnifying
optical system 76 housed in the casing 72 and disposed coaxially
with an optical axis extending along the Z-axis from the CCD camera
74. An electrically conductive movable tube 80 is mounted in a
lower end of the casing 72 by an air bearing 78. The movable tube
80 has on its upper end a gear 82 extending radially outwardly and
held in mesh with a .theta.-axis movable means (rotating means) 84
and a Z-axis movable means (moving means) 86.
[0037] The .theta.-axis movable means 84 has a fourth motor 90
fixed to a lower surface of a partition wall 88 disposed in the
casing 72 and the fourth motor 90 has a rotatable shaft 92 with a
gear 94 mounted thereon. The gear 94 is held in mesh with the gear
82 of the movable tube 80. The Z-axis movable means 86 has a fifth
motor 96 fixed to an upper surface of the partition 88 and the
fifth motor 96 has a rotatable shaft (not shown) to which a ball
screw 98 is connected. The ball screw 98 extends along the Z-axis
from the partition wall 88 to the lower end of the casing 72, and
is threaded through a vertically movable member 100 which supports
a lower end of the gear 82 of the movable tube 80.
[0038] The movable tube 80 supports in its lower end a
light-transmissive support disk (light-transmissive support member)
102 made of glass, synthetic resin, or the like to which there is
secured an electrically conductive tube 104 as a holder. The
movable tube 80 holds therein a light-transmissive cover member 106
spaced a distance upwardly from the support disk 102, the cover
member 106 and the support disk 102 defining a suction chamber 108
defined therebetween. The suction chamber 108 is connected to a
negative pressure source 111 through a hole 110 defined in a side
wall of the movable tube 80.
[0039] As shown in FIGS. 3 and 4, the support disk 102 has a
through hole 112 defined centrally therein and supports a
light-transmissive electrically conductive film 114 disposed on a
surface 102a thereof which faces the suction chamber 108. The
light-transmissive electrically conductive film 114 comprises a
large-diameter annular portion 114a extending along an outer
circumferential edge of the surface 102a, a small-diameter annular
portion 114b extending around the through hole 112, and a radial
straight portion 114c extending radially and interconnecting the
large-diameter annular portion 114a and the small-diameter annular
portion 114b. The light-transmissive electrically conductive film
114 has a thickness of, for example, 1 .mu.m.
[0040] As shown in FIGS. 3 and 5, the electrically conductive 20
tube 104 has a joining member 116 inserted in the through hole 112
in the support disk 102 and projecting a predetermined length from
the surface 102a. The joining member 116 is bonded to the surface
102a by an electrically conductive adhesive 117 such as silver
paste, for example. The joining member 116 has a tapered end
portion 118 held in contact with a surface 102b of the support disk
102 opposite to the surface 102a and progressively smaller in
diameter away from the surface 102b. The electrically conductive
tube 104 has an axial through hole 120 defined centrally
therein.
[0041] The axial through hole 120 has a diameter of 0.1 mm, and the
electrically conductive tube 104 has a maximum diameter of 1.55 mm
at its portion held in contact with the surface 102b, a minimum
diameter of 0.14 mm at its tapered end, and a length of 4 mm. These
dimensions are selected in view of the fact that each of the LED
chips 12 has a size of 0.3 mm.times.0.3 mm and an upper electrode
(described later on) thereof has a diameter of 0.17 mm. The
electrically conductive film 114 on the support disk 102 is
connected via the movable tube 80 to the negative terminal
(negative pole) of the DC power supply (not shown).
[0042] As shown in FIG. 1, an image processor (image processing
means) 130 for processing an image captured by the imaging means 20
to recognize the position of the light-emitting center of the LED
chip 12 is mounted on the mount base 32.
[0043] Operation of the bonding apparatus 10 will be described
below with reference to FIGS. 6 and 7.
[0044] As shown in FIG. 1, a plurality of LED chips 12 are disposed
in a two-dimensional pattern on the chip laying base 14, and the
board 22 coated with silver paste is placed on the bonding base 24.
The board 22 has an edge in the X-axis direction positioned in
alignment with a station reference surface (not shown). The board
22 is attracted to the bonding base 24 under a vacuum developed via
a suction hole (not shown) defined in the bonding base 24. The
light-emitting base 18 is connected to a positive terminal of an
unillustrated DC power supply.
[0045] The displacement mechanism 36 is actuated to displace the
chip laying base 14 to a position corresponding to the camera
center (collet center) of the imaging means 20, i.e., a chip
removal position, in step S1 (FIG. 6). Specifically, the first
motor 38 is energized to rotate the ball screw 48 about its own
axis to move the Y-axis movable table 50 along the Y-axis, and the
second motor 42 is energized to rotate the ball screw 54 about its
own axis to move the X-axis movable table 66 along the X-axis.
Therefore, when the first and second motors 38, 42 are energized,
one of the LED chips 12 on the chip laying base 14 is brought into
the chip removal position.
[0046] Then, the CCD camera 74 of the imaging means 20 captures an
image of the LED chip 12 on the chip laying base 14 in the chip
removal position in step S2. An image signal generated by the CCD
camera 74 and representing the LED chip 12 is supplied to the image
processor 130, which processes the image signal. Specifically, as
shown in FIG. 8, the image processor 130 recognizes the center O1
of an upper electrode 140 of the LED chip 12, and calculates a
deviation of the upper electrode center O1 from the center O of the
CCD camera, i.e., corrective quantities (.DELTA.X, .DELTA.Y) for
the LED chip 12 in step S3.
[0047] The calculated corrective quantities are compared with a
preset reference value in step S4. If the calculated corrective
quantities are greater than the preset reference value, then the
displacement mechanism 36 is actuated to move the LED chip 12 by
distances corresponding to the corrective quantities in step S5.
Specifically, the first motor 38 is energized to move the LED chip
12 by a distance corresponding to the corrective quantity .DELTA.Y,
and the second motor 42 is energized to move the LED chip 12 by a
distance corresponding to the corrective quantity .DELTA.X.
[0048] If the calculated corrective quantities are equal to or
smaller than the preset reference value, then the collet unit 16
attracts the LED chip 12 in step S6. Specifically, as shown in FIG.
2, the fifth motor 96 of the Z-axis movable means 86 in the casing
72 is energized to rotate the ball screw 98 about its own axis,
whereupon the vertically movable member 100 threaded over the ball
screw 98 is lowered. Since the gear 82 of the movable tube 80 is
supported on the vertically movable member 100, the movable tube 80
descends in unison with the vertically movable member 100 until the
tip end of the electrically conductive tube 104 contacts the LED
chip 12.
[0049] Thereafter, the negative pressure source 111 is actuated to
evacuate the electrically conductive tube 104 via the suction
chamber 108, thereby attracting the LED chip 12 against the tip end
of the electrically conductive tube 104. As shown in FIG. 9, the
third motor 66 is energized to rotate the ball screw 68 about its
own axis to lift the collet unit 16 together with the vertically
movable base 70, removing the LED chip 12 attracted by the
electrically conductive tube 104 upwardly from the chip laying base
14.
[0050] Then, the CCD camera 74 of the imaging means 20 captures an
image of the LED chip 12 attracted by the collet unit 16 in step
S7. The captured image of the LED chip 12 is processed by the image
processor 130, which recognizes an outer edge of the LED chip 12
and calculates a corrective quantity .DELTA..theta. in step S8. The
corrective quantity .DELTA..theta. is compared with a predetermined
reference value in step S9. If the corrective quantity
.DELTA..theta. is greater than the predetermined reference value,
control goes to step S10 in which the .theta.-axis movable means 84
is actuated for an angular interval corresponding to the corrective
quantity .DELTA..theta..
[0051] Specifically, as shown in FIG. 2, the fourth motor 90 of the
.theta.-axis movable means 84 is energized to rotate the gear 94
with the rotatable shaft 92, causing the gear 82 in mesh therewith
to rotate the movable tube 80 through an angle corresponding to the
corrective quantity .DELTA..theta. in a given direction. After the
LED chip 12 is angularly corrected for the corrective quantity
.DELTA..theta., the displacement mechanism 36 is actuated to move
the X-axis movable table 56 in the X-axis direction to bring the
light-emitting base 18 into alignment with the camera center of the
imaging means 20 in step S11 (FIG. 7).
[0052] The third motor 66 is energized to cause the vertically
movable base 70 to lower the collet unit 16 until a lower electrode
of the LED chip 12 attracted by the tip end of the collet unit 16
contacts the light-emitting base 18 in step S12, as shown in FIG.
10.
[0053] At this time, as shown in FIG. 11, the light-emitting base
18 is electrically connected to the positive terminal of the
non-illustrated DC power supply, and the movable tube 80 is
electrically connected to the negative terminal thereof. When a
current from the DC power supply is passed through the LED chip 12,
the LED chip 12 emits light in step S13. With the LED chip 12
emitting light, the CCD camera 74 captures an image of the
light-emitting state of the LED chip 12 via the cover member 106
and the support disk 102 in step S14. The CCD camera 74 sends an
image signal representing the light-emitting state of the LED chip
12 to the image processor 130, which recognizes the light-emitting
center of the LED chip 12 in step S15.
[0054] Specifically, as shown in FIG. 12, in a light-emission image
150 represented by the image signal read into the image processor
130, two or more edges of each side are detected by edge detecting
windows 152, and four sides 150a-150d of the light-emission image
150 are determined. Then, as shown in FIG. 13, points 154a-154d of
intersection of the sides, i.e., the corners of the light-emission
image 150, are determined, and a point of intersection of diagonal
lines 156a, 156b passing through the points 154a-154d of
intersection, i.e., a light-emitting center O2, is determined.
Thereafter, as shown in FIG. 14, corrective quantities (.DELTA.X,
.DELTA.Y) based on a deviation of the light-emitting center O2 from
the camera center O are calculated in step S16.
[0055] The LED chip 12 is then de-energized, and the collet unit 16
is lifted in unison with the vertically movable base 70 by the
third motor 66 in step S17. Control proceeds to step S18 in which
the displacement mechanism 36 is actuated to displace a certain
bonding position on the board 22 attracted by the bonding base 24
into alignment with the camera center O of the imaging means 20. If
the corrective quantities (.DELTA.X, .DELTA.Y) calculated in step
S16 are greater than a preset reference value (NO in step S19),
then control goes to step S20 in which the bonding position on the
board 22 is corrected with respect to the camera center O.
[0056] The third motor 66 is energized to lower the collet unit 16
to place the LED chip 12 attracted by the collet unit 16 in the
bonding position on the board 22 in step S21. Then, the LED chip 12
is bonded on the board 22 in step S22, as shown in FIG. 15.
[0057] The other LED chips 12 placed on the chip laying base 14 are
processed in the same manner as the processing in step S6 and
subsequent steps, so that the other LED chips 12 are successively
bonded on the board 22 at respective bonding positions thereon. In
this manner, the LED chips 12 are bonded on the board 22 at equal
intervals between their light-emitting centers. After all the
desired LED chips 12 have been bonded on the board 22, the board 22
is removed from the bonding base 24, and the silver paste is
heat-set by an electric oven, for example.
[0058] In the first embodiment described above, the
light-transmissive electrically conductive film 114 is disposed on
the light-transmissive support disk 102 which is made of glass,
plastic, or the like, and the electrically conductive tube 104 is
electrically connected via the electrically conductive film 114 to
the negative terminal of the DC power supply. The light-emitting
base 18 is electrically connected to the positive terminal of the
DC power supply.
[0059] When the LED chip 12 attracted by the electrically
conductive tube 104 is energized to emit light, the light-emitting
state of the LED chip 12 can reliably be imaged by the CCD camera
74 through the support disk 102 and the cover member 106.
Consequently, the light-emitting center of the LED chip 12
attracted by the electrically conductive tube 104 of the collet
unit 16 can accurately be recognized, and hence the LED chips 12
can be bonded on the board 22 highly accurately at equal intervals
between their light-emitting centers.
[0060] Each LED chip 12 removed from the chip laying base 14 by the
electrically conductive tube 104 is delivered to the light-emitting
base 18 and the board 22 while being attracted by the electrically
conductive tube 104. The LED chip 12 is prevented from being
positionally displaced as much as possible when held by and
detached from the electrically conductive tube 104. The LED chip 12
can be bonded quickly and efficiently with a highly simple process
and arrangement.
[0061] As shown in FIG. 5, the electrically conductive tube 104 has
the tapered end portion 118 which is progressively smaller in
diameter away from the surface 102b. Whereas the upper electrode
140 of the LED chip 12 has a diameter of 0.17 mm, the tip end of
the tapered end portion 118 has a diameter of 0.14 mm. Therefore,
when the light-emitting state of the LED chip 12 is imaged by the
CCD camera 74 through the magnifying optical system 76, the
electrically conductive tube 104 does not serve as an obstacle,
allowing the light-emitting state of the LED chip 12 to be
recognized reliably.
[0062] As shown in FIG. 2, the movable tube 80 incorporating the
support disk 102 which is rotatable by the .theta.-axis movable
means 84 and vertically movable by the Z-axis movable means 86 is
supported by the air bearing 78. Consequently, the movable tube 80
is allowed by the air bearing 78 to rotate and move vertically
smoothly and accurately.
[0063] The joining member 116 projects through the through hole 112
in the support disk 102 from the surface 102a. The joining member
116 and the surface 102a are bonded to each other by the
electrically conductive adhesive 117 such as silver paste, for
example, which covers the small-diameter annular portion 114b of
the electrically conductive film 114, as shown in FIG. 5.
Therefore, the longitudinal dimension of the joining member 116
does not need to be established with high accuracy. The
electrically conductive tube 104 and the support disk 102 can be
positioned relatively to each other easily and reliably simply when
the electrically conductive tube 104 is held closely against the
surface 102b of the support disk 102.
[0064] FIGS. 16 and 17 show a collet unit 180 of a bonding
apparatus according to a second embodiment of the present
invention. Those parts of the bonding apparatus shown in FIGS. 16
and 17 which are identical to those of the bonding apparatus
according to the first embodiment are denoted by identical
reference characters, and will not be described in detail
below.
[0065] As shown in FIG. 16, the collet unit 180 has a
light-transmissive support disk (light-transmissive support member)
182 which has a through hole 184 defined centrally therein. The
through hole 184 has a diameter of 0.1 mm, for example. The support
disk 182 supports a light-transmissive electrically conductive film
186 disposed on a surface 182b thereof opposite to a surface 182a
thereof which faces the suction chamber 108. As shown in FIG. 17,
the light-transmissive electrically conductive film 186 has a
radially inner portion surrounding the through hole 184 and extends
radially outwardly to an outer circumferential edge of the support
disk 182. The light-transmissive electrically conductive film 186
has a thickness of 100 .mu.m, for example. When the support disk
182 is mounted in the movable tube 80, the light-transmissive
electrically conductive film 186 is electrically connected to the
movable tube 80. The light-transmissive electrically conductive
film 186 has a holder 188 for directly attracting and holding the
LED chip 12 in its portion surrounding the through hole 184.
[0066] When the support disk 182 is lowered, the holder 188 of the
light-transmissive electrically conductive film 186 on the surface
182b of the support disk 182 is brought into direct contact with
the upper surface of the LED chip 12. With the LED chip 12
attracted under vacuum via the through hole 184, the DC power
supply connected to the light-transmissive electrically conductive
film 186 and the light-emitting base 18 supplies a current to
energize the LED chip 12 to emit light.
[0067] In the second embodiment, therefore, while the LED chip 12
is being attracted by the holder 188, the light-emitting center of
the LED chip 12 can be recognized reliably, and the LED chip 12 can
be corrected in position for quick and accurate bonding on the
board 22.
[0068] FIG. 18 shows a collet unit 200 of a bonding apparatus
according to a third embodiment of the present invention. Those
parts of the bonding apparatus shown in FIG. 18 which are identical
to those of the bonding apparatus according to the first embodiment
are denoted by identical reference characters, and will not be
described in detail below.
[0069] The collet unit 200 does not have a light-transmissive
electrically conductive film on a light-transmissive support disk
(light-transmissive support member) 202. Rather, an electrically
conductive member 206, such as an electrically conductive wire, for
example, has an end electrically connected to a joining member 205
of an electrically conductive tube 204 serving as a holder fixed to
the support disk 202, and an opposite end electrically connected to
the movable tube 80. The bonding apparatus according to the third
embodiment is relatively inexpensive because no light-transmissive
electrically conductive film is disposed on the light-transmissive
support disk 202.
[0070] In the first through third embodiments, the bonding
apparatus is used to bond the LED chips 12 on the board 22.
However, the bonding apparatus is applicable to the bonding of
various components such as minute chips such as SLDs whose
light-emitting centers need to be positioned highly accurately and
chips of monolithic arrays.
[0071] With the bonding method and apparatus according to the
present invention, while a light-emitting element is being held by
the holder of the light-transmissive support member from the
direction in which the light-emitting element emits light, the
light-emitting element is energized to emit light, and the
light-emitting state of the light-emitting element is imaged via
the light-transmissive support member to recognize the
light-emitting center of the light-emitting element. Therefore, the
light-emitting state of the light-emitting element can be observed
and detected accurately while the light-emitting element is being
held by the holder. The light-emitting element can thus be
positioned and bonded on the board at a desired bonding position
thereon to position the light-emitting center thereof highly
accurately. As a result, a highly accurate array of light-emitting
elements can be fabricated efficiently.
[0072] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
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