Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
2002-05-03
2004-03-30
Eckert, George (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S099000, C257S676000
Reexamination Certificate
active
06713877
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting diode using a flip-chip-type light-emitting element having a widened light-emitting surface.
2. Description of the Related Art
A conventional light-emitting diode
5
which uses a flip-chip-type semiconductor light-emitting element will be described with reference to
FIGS. 12 and 13
.
FIG. 13
is a vertical cross section schematically showing the appearance and structure of the conventional light-emitting diode
5
, which comprises a flip-chip-type semiconductor light-emitting element
100
(hereinafter referred to as the “flip chip
100
”).
FIG. 12
depicts a light-emitting element member
570
that is formed of a sub-mount
520
serving as a substrate and the flip chip
100
mounted thereon.
A lead frame
50
is composed of a metal post
51
and a metal stem
53
, which are used for application of voltage to the light-emitting element member
570
. The metal stem
53
has a reflection portion
55
and a flat portion
54
on which the light-emitting element member
570
is placed. A resin mold
40
encloses the light-emitting element member
570
. The bottom surface
527
of the light-emitting element member
570
is bonded to the metal stem
53
by use of silver paste or any other suitable material, to thereby be electrically connected thereto. An electrode
521
is formed on the sub-mount
520
to be located in an exposed portion
528
thereof. The electrode
521
is connected to the metal post
51
through wire bonding using gold wire
57
.
Light emitted by the flip chip
100
reflects off a positive electrode disposed on a first main face, passes through a sapphire substrate disposed on a second main face, and then radiates to the outside. Therefore, the flip chip
100
is mounted on the sub-mount
520
in a face-down orientation such that the first main face faces downward.
Next, the sub-mount
520
serving as a substrate will be described.
FIG. 12A
is a plan view of the sub-mount
520
before attachment of the flip chip
100
;
FIG. 12B
is a plan view of the sub-mount
520
after attachment of the flip chip
100
; and
FIG. 12C
is a cross sectional view of the sub-mount
520
after attachment of the flip chip
100
.
The sub-mount
520
is formed of, for example, an electrically conductive semiconductor substrate. The upper surface of the sub-mount
520
is covered with an insulation film
524
made of SiO
2
except for a portion
523
, to which an Au micro-bump
533
is soldered for establishing connection with the positive electrode of the flip chip
100
. A negative electrode
521
is formed on the insulation film
524
by means of aluminum vapor deposition. On the negative electrode
521
are defined a pad region in which the negative electrode
521
is wire-bonded to the metal post
51
and a region in which an Au micro-bump
531
is soldered to the negative electrode
521
in order to establish connection with the negative electrode of the flip chip
100
.
Conventionally, in order to perform wire bonding, there must be formed a circular bonding pad region having a diameter of at least 100 &mgr;m, or a square bonding pad region, each side of which has a length of at least 100 &mgr;m. In order to allow formation of the electrode
521
providing such a bonding pad region on the exposed portion
528
of the sub-mount
520
, as shown in
FIG. 12B
, the flip chip
100
having a square shape must be disposed on the sub-mount
520
at a position offset toward one side. That is, since the exposed portion
528
must be formed to have a predetermined area or greater, the flip chip
100
cannot be disposed on the sub-mount
520
such that the center P
2
of the flip chip
100
coincides with the center P
501
of the sub-mount
520
and the center axis (indicated by broken line B—B in
FIG. 12B
) of the flip chip
100
coincides with the center axis (indicated by broken line A—A in
FIGS. 12A and 12A
) of the sub-mount
520
. Further, when the light-emitting element member
570
is placed on the flat portion
54
having substantially the same area as the light-emitting element member
570
, the center axis A—A of the sub-mount
520
inevitably coincides with the center axis (indicated by broken line D—D in
FIG. 13
) of the reflection portion
55
having a parabolic shape.
As described above, the sub-mount
520
must have the exposed portion
528
in order to enable formation of the electrode
521
serving as a bonding pad which is used for wiring between the flip chip
100
and the metal post
51
. Therefore, the sub-mount
520
has a rectangular shape. In addition, the flip chip
100
is disposed on the sub-mount
520
in an offset manner, so that the center axis of the flip chip
100
deviates from the center axis of the reflection portion
55
of the lead frame
50
. Therefore, the conventional light-emitting diode
5
has a drawback in that luminous intensity changes with position of view; i.e., luminous intensity differs according to whether the diode
5
is viewed from the right side or left side, or from the upper side or lower side. Further, since the area of the flat portion
54
of the lead frame
50
is small, the area of the sub-mount
520
inevitably becomes small. Therefore, if there is employed a design in which the flip chip
100
is disposed on the sub-mount
520
such that the center axis of the flip chip
100
coincides with that of the rectangular sub-mount
520
, and the exposed portion for formation of an attachment electrode is secured, the size of the flip chip
100
decreases, so that a required luminance cannot be obtained.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a light-emitting diode which provides constant luminous intensity regardless of position of view.
Another object of the present invention is to provide a light-emitting diode in which the area of a flip chip is maximized in order to secure high luminance, while a region for an electrode for electrical connection is secured on a sub-mount.
Still another object of the present invention is to provide a light-emitting diode which has a reduced overall size and improved durability and which can be fabricated through a simplified fabrication process.
In order to achieve the above-described objects, according to a first aspect of the present invention, there is provided a light-emitting diode using a flip chip which is a flip-chip-type semiconductor light-emitting element, comprising: a rectangular flip chip; and a rectangular sub-mount on which the flip chip is placed. The sub-mount has a shorter side longer than a diagonal of the flip chip. The flip chip is placed on the sub-mount such that a side of the flip chip intersects a corresponding side of the sub-mount.
According to a second aspect of the present invention, there is provided a light-emitting diode using a flip chip which is a flip-chip-type semiconductor light-emitting element, comprising a substantially square flip chip; and a substantially square sub-mount on which the flip chip is placed. The flip chip is placed on the sub-mount at a position and posture which are obtained through superposition of a center point and center axis of the flip-chip on a center point and center axis of the sub-mount and subsequent rotation of the flip chip about the center points by a predetermined angle. Here the term of a substantially square means the figure including a parallelogram, a trapezoid, or a quadrangle which is slightly shifted from a right square.
According to a third aspect of the present invention, the predetermined angle is about 45 degrees.
According to a fourth aspect of the present invention, the sub-mount is formed of a semiconductor substrate, and a diode for over-voltage protection is formed within the semiconductor substrate.
According to a fifth aspect of the present invention, the diode for over-voltage protection is formed to be located below an upper exposed region of the sub-mount.
According to a sixth aspect of the present invention, the sub-mount is formed
Hirano Atsuo
Teshima Kiyotaka
Yasukawa Takemasa
Yoshikawa Yukio
Eckert George
McGinn & Gibb PLLC
Nguyen Joseph
Toyoda Gosei Co,., Ltd.
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