Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Encapsulated
Reexamination Certificate
1999-08-03
2001-10-30
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Encapsulated
C257S098000, C257S103000, C257S082000, C257S081000, C257S099000, C257S706000
Reexamination Certificate
active
06310364
ABSTRACT:
BACKGROUND OF INVENTION
Field of invention
This invention relates to a light-emitting apparatus having a GaN semiconductor light-emitting device. More particularly, the present invention relates to an improvement on a light-emitting apparatus having a semiconductor light-emitting device integrated by flip chip bonding.
GaN semiconductors have been attracting attention as a material for light-emitting device emitting blue to green light. A light-emitting diode comprising such a GaN semiconductor is incroporated into a light-emitting apparatus as follows. Since a general light-emitting diode uses an insulating sapphire substrate, a pair of electrodes (i.e., a negative electrode and a positive electrode) are provided on the upper side of the semiconductor layer.
A first lead frame has a mount, onto which a substrate or a light-emitting diode is adhered with the semiconductor layer up so that the semicoductor layer faces the dominant light emitting direction of the light-emitting apparatus. The negative electrode and the postive electrode of the light-emitting diode are connected to the first and second lead frames, respectively. These members are encapsulated in a transparent sealing resin, such as an epoxy resin.
In the above-described light-emitting apparatus, blue to green light generated in the light-emitting layer in the semiconductor layer is transmitted through the semiconductor layer and emitted outside or reflected on the mount of the first lead frame, transmitted through the semiconductor layer again, and emitted outside. Accordingly, the direction perpendicular to the semiconductor layer is the dominant light-emitting direction. For more details, JP-A-
7-23558
can be referred to.
However, conventional sealing resin, such as an epoxy resin, is liable to color change, and the color change is accelerated by beat. According to the inventor's study, a sealing resin is observed to undergo gradual color change to yellow to browm around a semiconductor layer that is accompanied by heat generation while emitting light. The resin thus yellowed or browned absorbs blue to green light emitted from the light-emitting diode. That is, the brightness of a light-emitting apparatus (the quantity of light emitted outside through the sealing resin) is reduced with the progress of color change of the sealing resin.
In order to solve this problem, flip chip bonding has been proposed, in which a light-emitting diode is reversed, and the negative and the positive elcetrodes are mounted directly on the lead frames by soldering, etc. For more detail, JP-A-56-79482 can be referred to. According to this structure, the heat generated from the light-emitting device is easily dissipated outside through the lead frames so that the color change of the sealing resin can be suppressed.
The distance between the negative and the positive electrodes is governed by the size of the light-emitting device, which is as small as about 350 &mgr;m. On the other hand, since a lead frame is formed by metal sheet working, the working precision is limited to the metal sheet thickness (e.g., 0.5 mn). Therefore, it is difficult to work a metal sheet in conformity to the distance between the electrodes of a light-emitting device. Assuming precise metal sheet working is possible, it is extremely difficult and impractical to fix the electrodes on the mounts of lead frames with positioning accuracy on the order of microns.
A light-emitting apparatus using a sealing resin having dispersed therein a fluoresent material to have the color of emitted light changed is known. For example, part of blue light generated from a light-emitting device is absorbed by the fluorescent material so that orange light is emitted from the fluorescent material. The blue light that does not pass through the fluorescent material and the orange light emitted from the fluorescent material are mixed up so that the Light-emitting device emits white light as a whole. However, it has been difficult with conventional Light-emitting apparatus of this type to secure color unchangeabililty of the emitted light for a long period of time because the sealing resin undergoes color change with time due to the heat generated in the Light-emitting device.
SUMMARY OF INVENTION
Accordingly, an object of the present invention is to settle the above-mentioned problem by providing on an industrial scale a light-emitting apparatus having a GaN semiconductor Light-emitting device incorporated therein in the form of a flip chip.
Another object of the invention is to provide a light-emitting apparatus having a novel structure.
Another object of the present invention will then be illustrated. This aspcet aims to provide a highly reliable Light-emitting apparatus with a new function. This Light-emitting apparatus according to this aspect is characterized in that the base contains a fluorescent material, with the construction of the other elements being the same as described later.
The above objects of the invention are accomplished by a light-emitting apparatus comprising (1) a transparent base made of an inorganic material, (2) a first and a second bonding pad formed on the base, (3) a GaN semiconductor Light-emitting device having a first and a second electrode on one side thereof, (4) a first wire and a second wire which connect the first bonding pad to the first electrode and the second bonding pad to the second electrode, respectively, (5) a first and a second lead frame, (6) a transparent adhesive layer which fixes the transparent substrate of the semiconductor Light-emitting device to a first surface of the base, and (7) a transparent resin which encapsulates the base, the Light-emitting device, the first and the second wires, the first and the second lead frames, and the adhesive layer, wherein the base is fixed to the first and second lead frames so that the substrate of the semiconductor Light-emitting device may face the dominant light-emitting direction or the Light-emitting apparatus, and the first and second bonding pads are electrically connected to the first and second lead frames, respectively.
According to this structure, the substrate (of the semiconductor Light-emitting device), the adhesive layer, the base, and the sealing resin are lying in this order on the light-emitting layer of the semiconductor Light-emitting device in the dominant light-emitting direction. Made of an inorganic material, the substrate and the base undergo little change in color. Most of the heat generated in the semiconductor layer during light emission is conducted to the other members and dissipated there before it reaches the sealing resin on the base. As a result, the sealing resin on the base is prevented from yellowing or browning by heat.
Only the adhesive layer undergoes color change under the influence of the heat of the semiconductor layer, but the influence of the heat upon the adhesive layer is lessened by the substrate interposed between the adhesive layer and the semiconductor layer. Therefore, the degree of the adhesive layer's color change is less than what would have been observed with the sealing resin directly covering the semiconductor layer in a conventional structure. Besides, because an adhesive layer can be made thin, the quantity of light that may be absorbed by a somewhat colored adhesive layer can be minimized.
The sealing resin covering the semiconductor layer naturally undergoes color change, but the influence of the color change is negligible because the colored portion is on the side opposite to the dominant LE side. Where the electrodes of the semiconductor Light-emitting device are formed of a light-emitting metal and cover the entire surface of the semiconductor layer, the light emitted from the LE layer in the direction opposite to the dominant light-emitting direction is reflected on these electrodes. Therefore, the colored resin portion is substantially out of the light transmission path.
According to the present invention, the semiconductor Light-emitting device is fixed on the base, and the base is attached to the first and second l
Lee Eddie
Lee Eugene
Pillsbury & Winthrop LLP
Toyoda Gosei Co,., Ltd.
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