Semiconductor light-emitting device

A semiconductor light-emitting device includes: a printed-wiring board; a light-emitting diode element mounted on the printed-wiring board; and a resin body for sealing the light-emitting diode element. The resin body is composed of a first resin body arranged around the light-emitting diode element, and a second resin body, which seals the light-emitting diode and the first resin body. An upper edge of the first resin body disposed at a lower position of the PN-junction is configured to be at least on or beyond an imaginary line that connects the PN-junction and a lower edge of the second resin body.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2007-8711, filed on Jan. 18, 2007, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light-emitting device using a light-emitting diode element.

2. Description of Related Art

Conventionally, in semiconductor light-emitting devices of surface mount type, it has been significant challenges to improve emission efficiency for the sake of extended battery life of intended apparatuses, as well as to achieve a further miniaturization. For improved emission efficiency, some devices are configured so that the periphery of light-emitting diode (hereinafter, abbreviated as LED) element, excluding its light-emitting surface, is covered with a white resin which has a high light reflectance and diffuse reflection effect. (For example, see Japanese Patent Application Laid-Open No. 2005-277227).

On the other hand, conventional light-emitting devices have left room for improvement regarding the effective use of light that is laterally and downwards emitted from a junction of the LED element.

In order to efficiently use light that is emitted from LED element downwards, many semiconductor light-emitting devices have a printed-wiring board that is plated with silver or the like to increase reflectance at the component side for the LED element to be mounted on. Since the LED element emits light radially from its junction, it is difficult to use downward light emitted from its junction efficiently unless the silver plating has a sufficient area. This has left a problem of miniaturization.

FIG. 8shows a conventional semiconductor light-emitting device70which incorporates an LED element60. The reference numeral71represents a printed-wiring board on which the LED element60is mounted. A pair of substrate electrodes72and73is formed on the top of this printed-wiring board71so as to wrap around both sides. A reflective film74made of metal with a high light reflectance, such as aluminum and silver, is formed on the surface of one substrate electrode73. Moreover, two element electrodes54and55of the LED element60are connected to the substrate electrodes72and73of the printed-wiring board71by wires75, respectively. The LED element60is sealed with a transparent or translucent resin body76. The outer periphery except a surface contact with an upper surface of the printed-wiring board of this resin body76is configured to be light-emitting surfaces77.

In the LED element60, its PN-junction53emits light of high intensity radially. Of the light emitted, emission light78that travels downward at steep angles from the PN-junction53is reflected by the reflective film74, and is thus directed upward with relatively high efficiency. Emission light79that travels slightly downwards from the PN-junction53is reflected by the substrate electrode73outside the reflective film74. Also, light emitted laterally and downwards without being reflected, refracts in further downward directions when being emitted out of the resin body76, and thus, the intensity of light emitted out of the light-emitting device70has room for improvement.

In view of bondability of the wires75, it is desirable to plate the surfaces of the substrate electrodes72and73with gold. The gold plating, however, has the problem of extremely low reflectance particularly for blue LEDs. As mentioned above, since the PN-junction53emits light of high intensity also downward, there has been a significant problem with emission efficiency in that much of light travels laterally downward like the emission light79.

FIG. 9shows a semiconductor light-emitting device for solving the foregoing problem, in which reflective films74aand74bare provided on the entire surfaces of the substrate electrodes72and73formed on the printed-wiring board71. Since the reflective films74aand74bare provided on the entire surfaces of the substrate electrodes72and73, both the emission light beams78and79are reflected by the reflective films74aand74b,thereby solving the problem of emission efficiency. However, provision of reflective films74aand74bsuch as aluminum and silver on the wire bonding surfaces can lower wire bondability and deteriorate reliability.

FIG. 10shows a semiconductor light-emitting device90for solving the problem in the reliability of the wire bonding, wherein the width of the semiconductor light-emitting device90is increased to widen the reflective film74. More specifically, the semiconductor light-emitting device90shown inFIG. 10is given a width L2greater than the width L1of the semiconductor light-emitting device70shown inFIG. 8(L1<L2). The width of the reflective film74is also increased accordingly. This configuration improves emission efficiency and enhances reliability of the wire bonding, whereas it counteracts the miniaturization.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor light-emitting device which has a small size but a high emission efficiency.

To achieve the foregoing object, a semiconductor light-emitting device according to the present invention includes: a printed-wiring board; an LED element mounted on the printed-wiring board; and a resin body for sealing the LED element, the resin body being composed of a first resin body arranged around the LED element, and a second resin body for sealing the LED element and the first resin body.

Moreover, the first resin body is given a height slightly lower than the position of a PN-junction of the light-emitting diode element. Also, regarding the first resin body, that has an upper edge configured by a top surface and a side surface, the upper edge of the first resin body is configured to be set at least on an imaginary line that connects the PN-junction of the LED element and a lower edge configured by a side surface and a bottom surface of the second resin body. It is preferable that the edge of the first resin body is set beyond the imaginary line that connects the PN-junction of the LED element and the lower edge of the second resin body.

In addition, the first resin body also has a diffuse reflection effect, with a light reflectance higher than that of the second resin body.

According to the present invention, it is possible to increase reflectance of the light emitted from the LED element, thereby providing a semiconductor light-emitting device which has a small size and a high emission efficiency.

It is also possible to increase the amount of light to be emitted from one LED element. Even in cases where a plurality of LED elements are required, the number of elements in use can thus be reduced to miniaturize the semiconductor light-emitting device for cost saving.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1shows a first embodiment of the semiconductor light-emitting device according to the present invention. The semiconductor light-emitting device1includes an LED element2, a printed-wiring board3on which the LED element2is mounted, and a resin body for sealing the LED element2on the printed-wiring board3.

A pair of substrate electrodes5and6is formed on the top surface3aof the printed-wiring board3so as to wrap around both sides. The LED element2is bonded to the top surface of one substrate electrode6with an adhesive (not shown). Moreover, a pair of element electrodes24and25of the LED element2is electrically connected to the substrate electrodes5and6by wires26, respectively.

In the present invention, the resin body is composed of: a first resin body7which is arranged to surround the LED element2mounted on the printed-wiring board3; and a second resin body8which seals the LED element2and the first resin body7on the printed-wiring board3. The second resin body8is made of a transparent or translucent epoxy resin or silicone resin. The outer periphery thereof except a surface contact with the printed circuit board3is used as light-emitting surfaces9. It should be noted that a fluorescent agent and the like may be mixed into the second resin body8. For example, when the LED element2is a blue light-emitting diode, a yellow fluorescent agent such as YAG can be mixed into the second resin body8so that white light is emitted from the light-emitting surface9of the semiconductor light-emitting device1.

In the present embodiment, the first resin body7is given a height lower than the position of the PN-junction23, which is the light-emitting surface of the LED element2. It is particularly desirable that the top surface7aof the first resin body7be located slightly lower than the position of the PN-junction as shown inFIG. 1. This configuration makes it possible for the top surface7aof the first resin body7to reflect much of the light that is emitted laterally and downwards from the PN-junction of the LED element2.

For utilizing light emitted from the LED element toward laterally and downwards as light reflected upward efficiently, the first resin body is preferably located slightly lower than the position of the PN-junction23and the top surface of the first resin body is preferably set as large as possible in the second resin body.

By the way,FIG. 2shows how to determine a lower limit of height of the first resin body for the sake of utilizing light emitted from the LED element toward laterally and downwards as light reflected upward.FIG. 2shows three types of the first resin body7b,7c,and7d,each type having a different area of top surface7e,7f,or7g. As a lower limit of each first resin body7b,7c,or7d,an edge7h,7i,7jof the first resin body is at least on an imaginary line15or beyond the line15connecting the PN-junction23of the LED element2and a lower edge of the second resin body.

Here, the upper edge7h,7i,7jof the first resin body is an upper edge between the top surface and the side surface of the first resin body, and the lower edge of the second resin body is a lower edge between a side surface and a bottom surface of the second resin body. In this way, it is possible to determine a lower limit of height of the first resin body in relation to an area of the top surface of the first resin body for possibilities of design freedom.

Moreover, in the present invention, the first resin body7has a light reflectance higher than that of the second resin body. As a means of increasing the light reflectance, the present invention provides the first resin body7with a diffuse reflection effect. Diffuse reflection refers to situations where light from a light source impinges on minute asperities formed on the surface of an object and is diffusely reflected by the same.

The formation of the first resin body7from a white resin can increase the diffuse reflection effect. Fillers such as titanium oxide, white ceramics, and surface-roughened aluminum or silver can also be mixed into the transparent or translucent resin to enhance the diffuse reflection effect.

As described above, the first resin body7highly effective in diffuse reflection is arranged close by the PN-junction23of the LED element2. Thus, even if the first resin body7has a small area, emission light beams11and12that travel obliquely downward from the junction23can both be reflected by the top7aof the first resin body7toward the light output surface9with high efficiency. This configuration can increase the reflectance of the light emitted from the LED element2, thereby achieving a semiconductor light-emitting device1which has a small size but a high emission efficiency. It should be noted that the semiconductor light-emitting device1can be confined within the same width L1as that of the semiconductor light-emitting device1shown inFIG. 8.

Also, as shown in an embodiment inFIG. 3, the LED element may be mounted directly on a top surface3aof a printed-circuit board3and electrically connected to substrate electrodes disposed on the printed-circuit board3by wires26.

FIG. 4shows a second embodiment of the semiconductor light-emitting device according to the present invention. The semiconductor light-emitting device10has almost the same configuration as that of the semiconductor light-emitting device1according to the foregoing first embodiment except that a reflective film13highly effective in diffuse reflection is formed on the top of the first resin body7. Like reference numerals will thus be given, and a detailed description thereof will be omitted. The reflective film13mentioned above is made of an evaporated film of metal having a high reflectance such as aluminum and silver. Alternatively, the top of the first resin body7may be plated. The plated surface can be roughened to enhance the diffuse reflection effect further.

In this way, when the reflective film13is formed on the top of the first resin body7, the emission light beams11and12emitted from the PN-junction23of the LED element2can be diffusely reflected toward the light output surface9with high efficiency.

It should be noted that fillers having a high coefficient of thermal conductivity can be mixed into the first resin body7to enhance the effect of heat radiation from the LED element2, the down side being a consequent drop in reflectance of the first resin body7. Accordingly, the mixing of fillers having a high coefficient of thermal conductivity into the first resin body7and the formation of the reflective film13on the top thereof can be combined to simultaneously provide both high light-emission efficiency and a high heat radiation effect.

FIGS. 5 and 6show a third embodiment of the semiconductor light-emitting device according to the present invention. The semiconductor light-emitting device30has almost the same configuration as that of the semiconductor light-emitting device according to the foregoing first embodiment except that side surfaces with a tilt of the second resin body8are surrounded by a frame31. Like reference numerals will thus be given, and a detailed description thereof will be omitted. As shown inFIG. 6, the inner side surfaces32of the frame31is tilted so as to spread out upward, and is provided with a reflective film or mirror finishing to improve the reflecting efficiency at the surface. This configuration can further enhance the emission efficiency of the light emitted from the LED element2. It should be noted that the reflective film or the mirror finishing on the inner periphery32can be omitted if the frame31is made of a material having a relatively high reflectance.

FIG. 7shows a fourth embodiment of the semiconductor light-emitting device according to the present invention. The semiconductor light-emitting device40deals with the case where a plurality of LED elements is mounted on the printed-wiring board3. For example,FIG. 5shows the case where two LED elements2aand2bare mounted. In this instance, the first resin body7which surrounds the LED elements2aand2bis also interposed between the two LED elements2aand2b.

This configuration can further enhance the emission efficiency of the semiconductor light-emitting device40having a plurality of LED elements2aand2b.For example, even if three or more LED elements are mounted on a single substrate of small area in a closely-packed state, it is possible to avoid a drop in emission efficiency and provide a semiconductor light-emitting device which has a high emission efficiency and a small size.

As has been described, according to the present invention, the resin body highly effective in diffuse reflection is arranged close by the PN-junction, so that the light emitted from the PN-junction can be reflected with high efficiency.

The present invention also provides the significant effect that a plurality of LED elements can be closely arranged on a printed-wiring board of small area while avoiding a drop in emission efficiency.

Although the preferred embodiments of the present invention have been mentioned, it should be noted that the present invention is not limited to these embodiments, and various changes and modifications can be made to the embodiments.