Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-01-28
2004-04-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S110000, C313S113000, C257S098000, C257S100000
Reexamination Certificate
active
06727643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a reflective light emitting diode (LED) having a reflective surface that reflects the light emitted from a reflective optical device, namely an LED element, thereby obtaining high external radiation efficiency. The invention also relates to a photodetector such as a reflective photodiode or a reflective phototransistor having a reflective surface that condenses and receives the light entering from an outside, thereby obtaining high photo-detecting rate. The invention also relates to a reflective photo-detecting/light-emitting device or the like having a pair of the LED and the photodetector. Hereafter, the reflective light emitting diode is referred to simply as “reflective LED.” The reflective photodiode is referred to simply as “reflective PD.” The reflective phototransistor is referred to simply as “reflective PT.”
In the specification, the LED chip itself is referred to as “LED element,” while an entire light emitting device including a sealing resin to mount an LED chip and an optical device such as a lens system, is referred to as “light emitting diode” or “LED.” In the same manner, the PD chip or PT chip itself is referred to as “photo-detecting element,” while an entire photo-detecting device including a sealing resin to mount a PD chip or PT chip and an optical device such as a lens system, is referred to as “photodiode” or “PD” or “phototransistor” or “PT.” The LED element, the photo-detecting element and the photo-detecting/light-emitting element combining them are referred to as “solid-state optical element.”
2. Description of the Related Art
A reflective light emitting diode (reflective LED) is known conventionally. The reflective LED has a lead mounting an LED element thereon. The lead and the LED element is sealed with a synthetic resin. A reflective surface shape is formed by molding at a light-emitting surface side of the LED element, while a radiation surface shape is formed by molding at a rear surface side of the LED element. Then, a reflective mirror is formed by evaporation of a metal such as a silver on a synthetic resin surface of the reflective surface shape.
As an example of such reflective LED, an LED is shown in FIG.
35
and
FIG. 36
which is disclosed in Japanese Laid Open Patent Publication (Kokai) 10-144966.
FIG. 35
is a plan view of an entire configuration of a conventional reflective LED.
FIG. 36
is a cross-section taken along the line XXXVI—XXXVI of FIG.
35
.
As shown in FIG.
35
and
FIG. 36
, a reflective LED
331
has a pair of leads
333
a
and
333
b
. An LED element
332
is mounted on a lower surface of the one lead
333
a
. A wire
334
bonds and electrically connects the other lead
333
b
and the LED element
332
. Thus structured lead portion is encapsulated by a transparent epoxy resin
336
to form a molded shape. The molded shape has a radiation surface shape
336
a
at a rear surface side of the LED element
332
and a reflection surface shape
336
b
at a light emitting surface side of the LED element
332
. A silver is vapor-deposited on the reflection surface shape
336
b to form a reflection mirror
335
.
In such structure of the reflective LED
331
, external radiant efficiency does not decrease as in a lens LED even if a light-condensing rate is increased. The LED
331
can obtain high external radiation property, which does not depend on light distribution property, by the reflection mirror
335
having a solid angle of about 2&pgr; steradian in relation to the LED element
332
. Therefore, the LED
331
has less dislocation of an axis and is particularly suitable for light-condensation/external-radiation. Moreover, the upper and lower optical surfaces can be easily shaped at the same time by a transfer mold. Therefore, the LED
331
is suitable for mass production, too. There have been many propositions about a structure of the reflective LED. Still, it is only such transfer molding type LED that can be mass-produced and that are actually supplied to a market.
However, the reflective LED
331
is adversely affected by temperature change, since coefficient of thermal expansion is very much different between the sealing resin and the vapor-deposited metal. Moreover, the LED
331
is structurally weak and subject to separation or delamination. Then, the metal material of the reflection mirror
335
may be peeled off from the sealing resin
336
, thereby causing wrinkles on the reflection surface. Thus, the LED loses a function of the reflection mirror. Therefore, the LED
331
cannot deal with a process in a reflow furnace or the like for mounting substrates in which large temperature change takes place. Thus, there is a problem that the LED
331
cannot be surface-mounted.
Furthermore, as shown in
FIG. 35
, lead extracting portions
337
a
,
337
b
of 1 to 1.5 mm long must be formed on the sealing resin
335
for providing a masking space to prevent short-circuit of the leads
333
a
,
333
b
at the time of vapor-deposition of the metal and for reinforcement of end portions at the time of perpendicularly bending the leads
333
a
,
333
b
. Therefore, a package of the reflective LED
331
needs extra dimension of 2 to 3 mm. Consequently, another problem arises that there is a limit in miniaturization and high-density mounting.
In addition, the LED requires higher heat radiation property. This is because, in general, if temperature of the LED element increases, a light output of the LED element decreases, and its life property deteriorates, too. Particularly, in case large current is conducted to the LED element, an active heat radiation property is needed. Therefore, the heat radiation property has been insufficient in the conventional reflective LED that has such a structure as the LED
331
.
The reflective LED
331
by the transfer molding uses a synthetic resin having large fluidity. Therefore, a metal mold requires high accuracy and it has been difficult to fabricate the metal mold. Moreover, it has been necessary to fabricate a metal mold for each of LEDs having different specification of light distribution. Furthermore, there is a problem that a kind of usable sealing resin is limited and that the sealing resin is easily yellowed thereby shortening the life particularly of a blue LED.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a reflective optical device that has durability against a temperature change, that is easy to be miniatured and that is excellent in heat radiation.
Another object of the present invention is to provide a reflective optical device such as a reflective LED and its manufacturing method that has high light condensation/radiation efficiency and little dislocation of an axis, that has durability against a temperature change, that has many choices of encapsulating materials to be used and that is excellent in mass-productivity.
Still another object of the present invention is to provide a reflective optical device such as a reflective LED and its manufacturing method that has high light condensation/radiation efficiency and little dislocation of an axis, that has durability against a temperature change and a physical contact so as to be surface-mounted, that is easy to be miniatured, that can change a light distribution without a new metal mold and that is excellent in mass-productivity.
According to a first aspect of the invention, there is provided a reflective light emitting diode (LED). The LED comprises: an LED element; a pair of leads for supplying an electric power to the LED element; a reflection mirror of concave shape facing a light emitting side of the LED element; and a radiation portion provided at a back side of the LED element. The LED element is mounted on one of the leads. The one of the leads is contacted with or disposed near the reflection mirror. At least one of the leads is insulated from the reflection mirror. The pair of the leads and the reflection mirror are made of a material having a high heat conductivity, respectively, so as to have a sufficient h
McGinn & Gibb PLLC
Toyoda Gosei Co,., Ltd.
Tran Thuy Vinh
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