Semiconductor light emitting device

A light emitting element is die-bonded to a portion of a lead frame exposed at the bottom of an opening formed at a top face of a resin package. A reflector to direct light emitted from the light emitting element towards a predetermined direction is attached to the top face of the resin package. Lead terminals are arranged so as to protrude from two opposite side regions of the resin package. A predetermined lead terminal among the plurality of lead terminals, connected to a portion where the light emitting element is die-bonded, is bent upwards, and soldered to the reflector by solder paste.

This nonprovisional application is based on Japanese Patent Application No. 2003-419585 filed with the Japan Patent Office on Dec. 17, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor light emitting devices, and more particularly, to a semiconductor light emitting device including a light emitting element.

2. Description of the Background Art

In general semiconductor light emitting devices employed as the illumination device of a camera, the backlight of a liquid crystal display device, and the like, much current is conducted to achieve higher luminosity. However, a large current flow to the semiconductor light emitting device will cause increase of the temperature of the light emitting element per se, leading to poor light emitting efficiency to degrade the light emitting element in the worst case.

Therefore, measures to release the heat generated at the light emitting element outside efficiently in order to lower the temperature of the light emitting element have been adopted. One such measure is to increase the area or the thickness of the lead frame to which the light emitting element is die-bonded. Another known measure is to replace the material around the light emitting element with a material of high heat conductance.

In order to achieve high luminosity in the semiconductor light emitting device, the method of directing the light emitted from a light emitting element to a specified direction is employed. A resin lens or a reflector is attached to direct light towards the specified direction.

Additionally, a semiconductor light emitting device having the aforementioned measures combined is proposed to emit light of higher luminosity towards a specified direction. By way of example, one such semiconductor light emitting device disclosed in Japanese Patent Laying-Open No. 2003-115615 will be described hereinafter. Referring toFIG. 15, a light emitting element103and a reflector105are provided on the surface of a substrate101. Two leads104aand104bof light emitting element103is soldered107to the wiring of substrate101. A predetermined resin109is provided at the region of leads104aand104band the region of reflector105.

In this semiconductor light emitting device, leads104aand104bare brought into direct contact with resin109to achieve heat dissipation by allowing the heat generated at light emitting element103to be conducted to reflector105via resin109.

Additionally, Japanese Patent Laying-Open Nos. 2002-176203 and 2003-197974 disclose a semiconductor light emitting device that achieves heat dissipation by conducting the heat generated at a light emitting element to a reflector via resin having high heat conductivity. The semiconductor light emitting device disclosed in Japanese Patent Laying-Open No. 2002-176203 has the reflector formed integrally with the lead to allow direct conduction of heat generated at the light emitting element to the reflector without the intervention of resin and the like.

The semiconductor light emitting devices set forth above had the following problems. If the heat generated at the light emitting element is to be conducted to a reflector via resin, the resin must be cured with the reflector fixed at a predetermined location with respect to the substrate and the light emitting element so as to achieve fixation between the reflector and the substrate. Therefore, a dedicated jig to position the reflector at predetermined site was required since heat conduction cannot be achieved efficiently if the position of the reflector is deviated. Furthermore, it was necessary to control the amount of resin during the fixation of the reflector so that the resin does not flow excessively to a region where resin is not required. In the case where the reflector and lead are formed integrally, the semiconductor light emitting device will have the reflector covered with mold resin since the reflector and lead are formed integrally from the beginning. Thus, there was the problem that heat cannot be released efficiently to the air from the reflector.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is to provide a semiconductor light emitting device that can achieve heat conduction reliably towards a reflector and that can release heat efficiently from the reflector to the air.

A semiconductor light emitting device according to the present invention includes a lead frame, a semiconductor light emitting element, a sealing member, and a reflector. The lead frame includes a plurality of lead terminals. The semiconductor light emitting element is die-bonded to the lead frame. The sealing member seals the lead frame such that each of the plurality of lead terminals and the semiconductor light emitting element are exposed. The reflector is attached to the sealing member to emit the light output by the semiconductor light emitting element towards one direction. A predetermined lead terminal among the plurality of lead terminals, connected to the region of the lead frame to which the semiconductor light emitting device is die-bonded, is arranged towards the side where the reflector is located to be connected to the reflector.

In accordance with such a configuration, a predetermined lead terminal connected to the region where the semiconductor light emitting device is die-bonded is connected to the reflector. Accordingly, the heat generated at the semiconductor light emitting element is reliably conducted to the reflector via the predetermined lead terminal. As a result, the heat conducted to the reflector can be released efficiently by the reflector.

In order to couple the reflector with the predetermined lead terminal by, for example, attachment, the reflector preferably includes an attach region to attach the predetermined lead terminal. Particularly, it is desirable that the predetermined lead terminal is fixed to the reflector by a conductive material.

The sealing member is formed having side regions facing each other. When the plurality of lead terminals are respectively arranged so as to protrude from the sealing member along one of the side regions facing each other, the predetermined lead terminal is preferably arranged at one end of the plurality of lead terminals respectively disposed along one of the side regions.

Accordingly, the predetermined lead terminal can be bent towards the region of the sealing member where the reflector is disposed without covering the semiconductor light emitting element exposed at the sealing member. The area of connection between the reflector and the predetermined lead terminal can be ensured to allow the reflector to be supported and fixed more stably.

Furthermore, in the case where there is another predetermined lead terminal connected to the portion of the lead frame to which the semiconductor light emitting element is die-bonded, that another predetermined lead terminal is preferably arranged at the other end of the plurality of lead terminals respectively disposed along one side region.

Accordingly, the predetermined lead terminal and the another predetermined lead terminal connected to the reflector are disposed such that the distance therebetween is greatest. As a result, the reflector can be supported and fixed more stably by the predetermined lead terminal and the another predetermined lead terminal.

In the above-described case where the lead frame includes another predetermined lead terminal connected to the region of the lead frame to which the semiconductor light emitting element is die-bonded, the sealing member includes side regions facing each other, and the predetermined lead terminals are arranged so as to protrude from the sealing member along respective side regions facing each other, the predetermined lead terminal and the another predetermined lead terminal are preferably disposed at a position where the distance between the predetermined lead terminal and the another predetermined lead terminal is greatest.

Accordingly, the reflector is supported and fixed more stably through the predetermined lead terminal and the another predetermined lead terminal by virtue of the predetermined lead terminal and another predetermined lead terminal connected to the reflector such that the distance between these lead terminals is greatest.

There is further provided a groove at a region of the sealing member where the reflector is located to receive the predetermined lead terminal. The depth of the groove is preferably set such that the surface of the predetermined lead terminal and the surface of the sealing member where the reflector is located is substantially on the same plane as the predetermined lead terminal received in the groove.

By setting the top face of the predetermined lead terminal substantially flush with the top face of the sealing member, the reflector is brought into contact with the sealing member in addition to the predetermined lead terminal. As a result, the reflector can be supported and fixed further stably by the predetermined lead terminal and sealing member.

Alternatively, the reflector can be formed by folding and bending a member that becomes the reflector. This member is formed integrally with the predetermined lead terminal in an unfolded manner, corresponding to an expansion plan.

In this case, the step of coupling the predetermined lead terminal with the reflector is no longer required. Since the reflector is formed integrally with the leading end of the predetermined lead terminal, the reflector can be supported reliably by the predetermined lead terminal.

Such a member to constitute a reflector specifically includes a reflector body and another reflector body, a projection provided at one of the reflector body and the another reflector body, and a notch provided at the other of the reflector body and the another reflector body. In the reflector, the projection preferably engages with the notch.

In the case where the reflector is provided as a separate piece without being formed integrally with the leading end of the predetermined lead terminal, the degree of freedom of the configuration of the reflector is increased. For example, in the case where there is another sealing member that seals another lead frame to which another semiconductor light emitting element is die-bonded, the reflector can be disposed so as to bridge between the sealing member and the another sealing member.

Furthermore, the reflector preferably includes at least one of a flat portion and a curved portion as the region to reflect light from the standpoint of improving the degree of freedom of light reflection.

Specifically, a reflector can be used having a reflection plane whose configuration in cross section parallel to the optical axis is formed of a straight line, or a reflection plane whose configuration in cross section parallel to the optical axis is formed of a curve constituting a parabola, a portion of an ellipse, or an arc. Furthermore, a reflector can be used whose configuration in plane in a direction substantially orthogonal to the optical axis is a rectangle, a shape formed of two arcs and a straight line connecting these arcs, a shape corresponding to a portion of the curve of an ellipse or a parabola being partially coupled, or the like.

In order to release heat efficiently from the reflector to the air, preferably the entire reflector is exposed to the air.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Referring toFIGS. 1 and 2, a semiconductor light emitting device according to a first embodiment of the present invention has an opening10formed at a top face of a resin package3. A light emitting element2is die-bonded to a region of a lead frame1exposed at the bottom of opening10. At a top face of resin package3, a reflector5is attached to direct the light emitted by the light emitting element2towards a predetermined direction. Reflector5is attached such that its entirety is exposed to the air.

Respective lead terminals4aand4bof lead frame1are disposed so as to project from each of the two opposite side regions of resin package3. Among the plurality of lead terminals4aand4b, a predetermined lead terminal4aconnected to the region where light emitting element2is die-bonded is bent upward. The leading end of the bent lead terminal4ais soldered by, for example, solder paste6to a fringe portion identified as an attach region5aof reflector5. The remaining lead terminals4bare respectively bent downwards for connection to the wiring (not shown) formed at the substrate. Lead terminal4bis electrically connected to light emitting element2via leads2aand2b.

The two lead terminals4aconnected to reflector5are disposed diagonally opposite to each other at resin package3such that the distance between these two lead terminals is greatest.

In the above-described semiconductor light emitting device, lead terminal4aconnected to the region where light emitting element2is die-bonded is connected to reflector5. Accordingly, the heat generated at light emitting element2is reliably conducted to reflector5via lead terminal4a. The heat conducted to reflector5is released efficiently to the air by reflector5that is entirely exposed to the air.

By the efficient dissipation of heat generated at light emitting element2through reflector5, a relatively large current can be conducted to light emitting element2to allow increase of the luminosity. Furthermore, temperature increase of the light emitting element is suppressed to improve the reliability of light emitting element2. Additionally, degradation of light emitting element2can be suppressed.

The two lead terminals4aconnected to reflector5are disposed on the diagonal of resin package3. Accordingly, reflector5is supported by lead terminals4adisposed such that the distance therebetween is greatest. As a result, reflector5can be supported and fixed more stably by the lead terminals4a.

The present embodiment was described based on an example where lead terminal4aand reflector5are connected by solder paste6. Alternatively, appropriate conductive paste such as silver (Ag) paste can be used. The conductive paste has high heat conduction by the inclusion of metal particles.

The foregoing semiconductor light emitting device is described based on an example where respective lead terminals4aand4bare disposed projecting from two opposite side regions of resin package3. Alternatively, the semiconductor light emitting device may have the lead terminals respectively disposed so as to protrude from only one of the side regions of the resin package.

In this case, the two lead terminals4aconnected to reflector5are preferably disposed at one end and the other end such that the distance between these two lead terminals is greatest. Accordingly, reflector5can be supported and fixed more stably by the two lead terminals4a.

The number of lead terminals connected to the reflector is not limited to two; and three or more, or only one can be provided. Particularly in the case where only one lead terminal is connected to the reflector, the endmost lead terminal is preferably connected to the reflector. Accordingly, the lead terminal can be bent up towards the top face of the resin package while opening10(refer toFIG. 1) provided at the top face of resin package3is not covered. The reflector can be supported and fixed more stably while ensuring a connecting area between the reflector and lead terminal.

Second Embodiment

A semiconductor light emitting device according to a second embodiment of the present invention is directed to fixing the reflector more stably to the resin package.

Referring toFIGS. 3 and 4, a groove3ais formed in advance at the top face of resin package3such that the top plane of lead terminal4ais substantially flush with the top face of resin package3with lead terminal4aconnected to reflector5(refer toFIG. 1) in a bending status. The remaining configuration of the semiconductor light emitting device of the second embodiment is similar to the semiconductor light emitting device shown inFIG. 1. Therefore, the same elements have the same reference characters allotted, and description thereof will not be repeated.

In the semiconductor light emitting device of the second embodiment, lead terminal4aconnected to reflector5is received in groove3aprovided at the top face of resin package3by being bent towards the top face of resin package3. Accordingly, the top face of lead terminal4ais substantially flush with the top face of resin package3, so that reflector5is brought into contact with the top face of resin package3in addition to lead terminal4a. As a result, reflector5is supported and fixed further stably by both the top faces of lead terminal4aand resin package3, as compared to the foregoing semiconductor light emitting device.

In the semiconductor light emitting device of the second embodiment, lead terminal4ain a bent status will not protrude above the top face of resin package3. Therefore, the semiconductor light emitting device prior to attachment of a reflector can be handled easier.

Third Embodiment

A semiconductor light emitting device according to a third embodiment of the present invention has a reflector formed integrally with the lead frame. Referring toFIG. 5, a portion to become reflector5is formed integrally with the leading end of lead terminal4a. This portion to become the reflector is formed in a state (shape) in which the reflector is spread out in an unfolded manner corresponding to an expansion plan, including four reflector bodies55in the present embodiment.

A projection55ais provided at one of adjacent reflector bodies55. A notch55bto be engaged with projection55ais provided at the other of the adjacent reflector bodies55.

By bending each reflector body55and holding projection55aof reflector body55under engagement with notch55bof an adjacent reflector body55, reflector5is assembled. A semiconductor light emitting device having reflector5at the top face of resin package3is obtained, as shown inFIG. 6. The remaining elements are similar to those of the semiconductor light emitting device ofFIG. 1. Therefore, corresponding elements have the same reference characters allotted, and description thereof will not be repeated.

In the semiconductor light emitting device of the third embodiment, the portion to become reflector5is formed integrally with the leading end of lead terminal4a, taking a configuration in which reflector5is spread out in an unfolded manner corresponding to an expansion plan. Therefore, the step of connecting lead terminal4awith reflector5is not longer necessary. Assembly of the portions constituting the reflector leads to a state where reflector plate5is attached integrally to the leading end of lead terminal4a. As a result, reflector5is reliably supported and fixed to lead terminal4a.

Since reflector plate5and lead terminal4aare connected integrally, higher heat conduction is achieved, as compared to the case where the reflector plate is attached to the lead terminal. Thus, heat dissipation can be effected more efficiently.

The semiconductor light emitting device set forth above was described based on an example having a flat reflection plane for the reflector. Alternatively, a reflector having a curved reflection plane can be employed depending upon the shape in which the reflector is spread out in an unfolded manner and the assembly by, for example a bending process.

Fourth Embodiment

A semiconductor light emitting device including a plurality of resin packages in which a light emitting element is incorporated will be described here as a semiconductor light emitting device of the fourth embodiment. Referring toFIG. 7, reflector5is disposed so as to bridge across two resin packages3. A lead terminal4aconnected to the portion where a light emitting element (not shown) is die-bonded is connected to reflector5, likewise the semiconductor light emitting device described above.

By providing reflector5separately from the lead frame in the semiconductor light emitting device set forth above, the degree of freedom for attaching reflector5becomes higher. One reflector5can be attached with respect to two resin packages3. Since lead terminal4acoupled to the region where light emitting element2is die-bonded is connected, the heat generated at light emitting element2can be released efficiently by reflector5. As a result, the heat conducted to reflector5can be released efficiently through reflector5.

The above embodiment was described based on an example in which one reflector5is provided for two resin packages3. The number of resin packages3is not limited to two. A semiconductor light-emitting device having one reflector arranged for three or more resin packages can be provided.

The semiconductor light emitting devices of respective embodiments set forth above were described based on an example in which reflector5has a reflection plane whose configuration in cross section along an optical axis11is formed of a straight line, as shown inFIG. 8. Additionally, a reflector5having a reflection plane whose configuration in cross section is formed of a curve constituting a parabola or a portion of an ellipse can be disposed at the resin package, as shown inFIG. 9. Alternatively, a reflector5having a reflection plane whose configuration in cross section is formed of a curve constituting an arc can be disposed at the resin package, as shown inFIG. 10.

The semiconductor light emitting devices of respective embodiments set forth above were described based on an example in which reflector5whose configuration in plane in a direction substantially orthogonal to the optical axis is a rectangle. Additionally, in the case where two light emitting elements2are arranged, a reflector5whose configuration in plane in a direction substantially orthogonal to the optical axis is an ellipse with a major axis set along the direction where the two light emitting elements are arranged can be disposed at resin package3, as shown inFIG. 11.

Furthermore, a reflector5whose configuration in plane takes a shape formed of two arcs and a straight line connecting these arcs can be disposed at resin package3, as shown inFIG. 12. Alternatively, a reflector5whose configuration in plane takes a shape corresponding to a portion of the curve of an ellipse, a parabola or the like being coupled, can be disposed at resin package3, as shown inFIG. 13.

In a reflector whose configuration in plane in a direction substantially orthogonal to the optical axis is a rectangle, the four sheet-like reflection planes are preferably disposed in an inclined manner such that each spreads upwards, as shown inFIG. 14. Accordingly, light emitted from the light emitting element can be output efficiently in one direction.

By providing the reflector as a separate piece with respect to the lead frame, the shape of the reflector can be selected in accordance with the semiconductor light emitting device. The degree of freedom of the emission property of light output from the light emitting element becomes higher. Furthermore, with regards to a common semiconductor light emitting device prior to attachment of a reflector, various reflectors can be applied.