Semiconductor light emitting device

A semiconductor light emitting device is provided which comprises a metallic support plate 1; a semiconductor light emitting diode chip 2 mounted on a support surface 13a defined on an upper surface 13 of support plate 1; wiring conductors 4 mounted on side and upper surfaces 12, 13 of support plate 1 via insulators 6; and a plastic encapsulant 3 for sealing side and upper surfaces 12 and 13 of support plate 1 and a part of wiring conductors 4. As support plate 1 comprises at least one projection 16 extending from side surface 12 of support plate 1 through a notch 3a formed in plastic encapsulant 3 for outward exposure, heat from diode chip 2 can be efficiently diffused to the outside through projections 16 of support plate 1 extending through notch 3a of plastic encapsulant 3 for outward exposure, when heavy current flows through diode chip 2 through wiring conductors 4 for stronger lighting. Also, the device can selectively be mounted on a circuit board in either of the horizontal and vertical mounting structures by selectively disposing bottom surface 14 or projections 16 of support plate 1 in face of a mounting surface of circuit board and connecting lead terminal 4d of wiring conductor 4 to circuit board to direct light from diode chip 2 perpendicularly or parallel to circuit board.

TECHNICAL FIELD

This invention relates to a semiconductor light emitting device, in particular of the type capable of efficiently radiating heat from a semiconductor light emitting element through a support plate to the outside and of being mounted on a circuit board in the selected one of the horizontal and upright conditions for vertically or horizontally directing the light from light emitting element.

BACKGROUND OF THE INVENTION

Japanese Patent Disclosure No. 11-340517 discloses a semiconductor light emitting device which comprises an insulating substrate formed with wiring conductors, a semiconductor light emitting element attached on a main surface of the substrate, a reflector (a light reflecting plate) surrounding the semiconductor element on the substrate, and a light-transmissible plastic encapsulant for sealing the semiconductor element and reflector wherein the insulating substrate of the semiconductor light emitting device is mounted on a circuit board in the horizontal condition.

FIG. 12illustrates a known semiconductor light emitting device or light emitting diode which comprises an insulating substrate100, an island wiring conductor or die pad120and a terminal wiring conductor or bonding pad130formed separately from each other on a main surface101of insulating substrate100, an semiconductor element or light emitting diode chip140secured on island wiring conductor120, a lead wire150for electrically connecting an electrode on an upper surface of semiconductor element140and terminal wiring conductor130, and a light-transmissible plastic encapsulant160for sealing each portion of island and terminal wiring conductors120,130on main surface of insulating substrate100, semiconductor element140, and lead wire150.

Island and terminal wiring conductors120,130extend outwardly on main surface101of substrate100, then are bent downwardly along each end surface103,104and moreover are bent along a bottom surface102of substrate100to form bottom contact electrodes. Light emitted from an upper or side surface of diode chip140is irradiated to the outside through plastic encapsulant160. The shown light emitting diode device can be surface-mounted in the horizontal condition on a circuit board (not shown) with bottom surface102of substrate100in contact to the circuit board.

This light emitting diode device comprises a reflector110on main surface101of substrate100for surrounding diode chip140. Substrate100is formed of glass fiber into a plate of the rectangular section with flat main and bottom surfaces101,102, and the plate is impregnated with resin. Island and terminal wiring conductors120,130are formed by plating nickel and gold in turn on copper base materials attached to substrate100according to a printing technique. Island wiring conductor120comprises an island121formed on main surface101of substrate100, an island electrode122extending from one end of main surface101of substrate100through end surface103to one end of bottom surface102, and a narrow island wiring123on main surface101of substrate100for electrically connecting island121and island electrode122.

Terminal wiring conductor130comprises a terminal131on main surface101of substrate100, a terminal electrode132extending from the other end of main surface101of substrate100through end surface104to the other end of bottom surface102, and a terminal wiring133on main surface101of substrate100for electrically connecting terminal131and terminal electrode132. Terminal131is disposed out of a central line108to reduce a longitudinal length of substrate100for manufacture of light emitting diode in smaller size with reflector110that has a ring portion111on main surface101of substrate100.

Semiconductor light emitting element140is a gallium compound semiconductor such as gallium arsenic (GaAs), gallium phosphorus (GaP), gallium aluminum arsenic (GaAlAs), aluminum gallium indium phosphorus (AlGaInP), etc. A bottom electrode (not shown) formed on a bottom surface of light emitting element140is secured substantially on a central portion of island121through an electrically conductive bonding agent. An upper electrode (not shown) on an upper surface of light emitting element140is connected to terminal131through lead wire150striding over ring portion111of reflector110.

Reflector110has a ring portion111and flange portions112provided on opposite outer sides of ring portion111and is formed of liquid crystal polymer or ABS resin blended with white powder. Formed inside of ring portion111of reflector110is a reflecting surface113which is upwardly diverged or flaring to form a portion of conical, spherical or paraboloidal surface or similar surface thereto or combined surfaces thereof. A bottom end of reflecting surface113is positioned within island121to dispose light emitting element140inside reflecting surface113of ring portion111which is higher than light emitting element140. Ring portion111is formed on the outer periphery of island121, inner end of island wiring123and inner end of terminal131. Flange portions112of reflector110are formed along opposite sides105,106of substrate100and extends inwardly or widthwise to merge with ring portions111.

Plastic encapsulant160comprises a pair of ramp surfaces161,162which are positioned respectively inside of wiring conductors124,134, and incline respectively relative to end surfaces103,104at a given angle, a pair of vertical surfaces163,164which are substantially flush respectively with side surfaces of substrate100, and a flat top surface165between and substantially normal to vertical surfaces163,164. As seen inFIG. 12, plastic encapsulant160seals island121, terminal131, each inner portion of island and terminal wirings123,133, reflector110, light emitting element140and lead wire150, except wiring conductors124,134, and each outer portion of island and terminal wirings123,133. Each flange portion112of reflector110has a bare side surface114which is flush with side surface105or106and vertical surface163or164of plastic encapsulant160. Island and terminal electrodes122,132and each outer end of terminal wirings123,133extend out of plastic encapsulant160.

Recent attempts have been made to adopt such semiconductor light emitting devices as light sources for traffic signals or rear lumps of automobile, and in this case, semiconductor light emitting devices must produce the greater light output for a viewer to certainly and visually observe turning on or off of the light source from an off position. To this end, new high power light emitting semiconductors have already been developed to produce a high intensity light when relatively large electric current for example more than 350 mA (milliamperes) is supplied to the light emitting semiconductor element. However, when the element is activated with a large electric current over 350 mA, it may heat a surface of the element to a temperature above 150° C. Accordingly, prior art semiconductor light emitting device cannot produce a high light output because heat from the light emitting semiconductor element cannot efficiently be diffused or radiated.

Also, there is another attempt for adapting the semiconductor light emitting device of this kind to a backlight source for a liquid crystal panel or the like. Such an application of the device requires a vertical mounting structure of the device capable of directing light from light emitting element parallel to a mounting surface of a circuit board on which the device is attached. Simultaneously, the device is also required to selectively form a horizontal structure capable of directing light from light emitting element perpendicularly to the mounting surface of circuit board. Accordingly, two kind of prior art semiconductor light emitting devices had to separately be formed into vertical and horizontal mounting structures with different package configurations in response to vertical and horizontal mounting on circuit board. It is therefore desirable to develop a semiconductor light emitting device of a single configuration selectively applicable to vertical and horizontal mounting.

An object of the present invention is to provide a semiconductor light emitting device capable of efficiently diffusing heat from a semiconductor light emitting element to the outside through a support plate for bearing the light emitting element when heavy current flows therethrough for stronger lighting. Another object of the present invention is to provide a semiconductor light emitting device of a single configuration selectively applicable to vertical and horizontal mounting. Still another object of the present invention is to provide a semiconductor light emitting device which can improve light directivity and axial brightness or luminance. A further object of the present invention is to provide a semiconductor light emitting device which may be manufactured by preferably injecting and filling resin within interior of reflector in forming a plastic encapsulant.

SUMMARY OF THE INVENTION

The semiconductor light emitting device according to the present invention comprises a metallic support plate (1); at least one semiconductor light emitting element (2) mounted on a support surface (13a) defined on an upper surface (13) of the support plate (1); at least one wiring conductor (4) mounted on side and upper surfaces (12,13) of the support plate (1) via an insulator (6); and a plastic encapsulant (3) for sealing at least a portion of side and upper surfaces (12,13) of the support plate (1) and a part of said wiring conductor (4). Support plate (1) comprises at least one projection (16) extending from side surface (12) of support plate (1) through a notch (3a) formed in plastic encapsulant (3) for outward exposure, and a bare bottom surface (14) unsealed by plastic encapsulant (3). Wiring conductor (4) has a junction end (4c) electrically connected to an electrode on semiconductor light emitting element (2) and a lead end (4d) extending to the outside of plastic encapsulant (3). When heavy current flows through semiconductor light emitting element (2) through wiring conductor (4) for intenser or stronger lighting, heat from light emitting element (2) can be efficiently diffused to the outside through projection (16) of support plate (1) extending through notch (3a) of plastic encapsulant (3) for outward exposure. Also, the device can selectively be mounted on a circuit board in either of the horizontal and vertical mounting structures by selectively disposing bottom surface (14) or projection (16) of support plate (1) in face of a mounting surface of circuit board and connecting lead end (4d) of wiring conductor (4) to circuit board to direct light from semiconductor light emitting element (2) perpendicularly or parallel to circuit board. Embedded portion of wiring conductors (4) in plastic encapsulant (3) extends along side and upper surfaces (12,13) of support plate (1) through insulator (6) without interfering electrical connection by wiring conductor (4) between projection (16) of support plate (1) and circuit board for vertical mounting of the device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of high power light emitting diodes (LED) according to the present invention are described hereinafter with reference toFIGS. 1 to 11of the accompanying drawings.

Referring now toFIGS. 1 to 3, a light emitting diode according to the present invention, comprises a metallic support plate1; eight light emitting diode chips2as semiconductor light emitting elements mounted on a support surface13aformed on an upper surface13of support plate1; sixteen wiring conductors4attached on long side and upper surfaces12aand13of support plate1through insulators6and extending from both side surfaces12ato the outside away from light emitting diode chips2; and a plastic encapsulant3sealing side and upper surfaces12aand13of support plate1and each inner portion of wiring conductors4.

Support plate1is formed of a metallic material such as copper, aluminum or copper alloy or aluminum alloy having the thermal conductivity equal to or more than 190 kcal/mh ° C. Such high thermal conductivity can directly or effectively release heat from light emitting diode chips2to the outside through support plate1when diode chips2is turned on with heave current passing through diode chips2and wiring conductors4to make diode chips2give out light with high luminance or brightness corresponding to the heavy current. In this way, metallic support plate1enables diode chips2to emit light with heavy current equal to or more than 350 mA, whereas an actual structure which incorporates a prior art light emitting diode has its relatively high thermal resistance on the order of 400° C., and the diode chips are operated with a drive current of approximately 20 mA.

FIGS. 1,2and3show respectively side, plan and bottom views of a light emitting diode according to the present invention, andFIGS. 4 and 5illustrate respectively sectional views taken along lines IV—IV and V—V inFIGS. 1 to 3. As understood fromFIGS. 1 to 5, support plate1in this embodiment is formed into a substantially rectangular shape having a pair of opposite long side surfaces12aand a pair of opposite wide or short side surfaces12b. Support plate1is formed with a substantially rectangular hole1agrooved in a spaced relation to long and short side surfaces12aand12b. Support plate1has a support surface13aon which light emitting diode chips2are mounted within hole1a, and a pair of beveled or inclined surfaces1bfor defining hole1aand surrounding diode chips2. A pair of divergently inclined surfaces1bhave an upwardly increasing spaced distance between them away from support surface13ato provide a light catoptrical or repercussive reflector for improvement in directivity and axial luminance of light from light emitting diode chip2.

As shown inFIGS. 3 and 4, support plate1comprises projections16extending outward from long side surfaces12abetween upper and bottom surfaces13and14of support plate1, and a bottom surface14uncovered from plastic encapsulant3. Each projection16has the same height as that between upper and bottom surfaces13and14of support plate1, but height, length and width of projections16can be selected as necessary, and also, projections16may be formed in an area of the middle or upper height or long side surfaces12anear upper surface13and away from bottom surface14of support plate1. As shown inFIG. 1, support plate1of this embodiment comprises projections16which each has a relatively wide protrusion16aformed at a substantially longitudinal center on a long side surface12a; and a pair of relatively narrow protrusions16bon the opposite ends of long side surface12aconnected to short side surfaces12b.

Wiring conductors4are made of for example highly conductive metal such as copper, each of which comprises a junction terminal4celectrically connected to an upper electrode of light emitting diode chip2; and a lead terminal4dextending outward from plastic encapsulant3. Each wiring conductor4is formed with a bent portion4eat the corner of upper and long side surfaces13and12ato mount it on upper and long side surfaces13and12aof support plate1through insulator6.

Plastic encapsulant3is formed of opaque or translucent resin having the high softening point and relatively high content of an additive compound or filler such as silica. When plastic encapsulant3is formed of heat resistive and thermosetting black epoxy resin applied to packages for power transistors and including relatively higher content of such compound than that of light transmissible resin, bonding or sealing property of plastic encapsulant3hardly changes or deteriorates even if heat from light emitting diode chip2is continuously exerted on plastic encapsulant3. Accordingly, even in case that heat is radiated from light emitting diode2and there is difference in coefficient of thermal expansion between plastic encapsulant3and wiring conductors4, no clearance or gap is disadvantageously formed in contact areas between plastic encapsulant3and wiring conductors4for long environmental resistance and highly reliable quality of the high power light emitting diode. For example, plastic encapsulant3may be formed of white epoxy resin having the improved resistance against heat or ultra-violet ray by blending filler such as silica, titanium or boron nitride into the resin.

As shown inFIGS. 1 and 5, plastic encapsulant3of this embodiment seals a part of upper surface13and cutouts14aformed with bottom surface14of support plate1to firmly secure plastic encapsulant3to support plate1and prevent exfoliation thereof from support plate1. As shown inFIGS. 2 and 5, plastic encapsulant3has a pair of divergently beveled or inclined surfaces3dformed along long side surfaces12a, and inclined surfaces3dhave an upwardly increasing spaced distance between them away from upper surface13of support plate1to provide a light catoptrical or repercussive reflector for improvement in directivity and axial luminance of light from light emitting diode chip2. Also, plastic encapsulant3has a pair of flat vertical surfaces3eformed along short side surfaces12b. Accordingly, hole1aformed by beveled surfaces1bof support plate1is upwardly continuously extended by divergently inclined surfaces3dand flat vertical surfaces3eof plastic encapsulant3to fill the whole hole1awith transparent or translucent protective resin5of high refractive index and high light transmission such as heat resistive silicone resin. Protective resin5serves to preserve light emitting diode chips2and lead wires8electrically connecting upper electrode of diode chips2and wiring conductors4. Also, coating material such as light transmissible polymetaloxane or ceramics may be filled in hole1adefined by inclined surfaces1bof support plate1, inclined surfaces3dand vertical surfaces3eof plastic encapsulant3. In another aspect, light emitting diode device of the invention may be formed without protective resin5.

As illustrated inFIGS. 1 and 4, plastic encapsulant3is formed with cutouts3athrough which projections16extend from each long side surface12aof support plate1for outward exposure so that the number of cutouts3ais the same as that of projections16. In this way, projections16can effectively release a full amount of heat from light emitting diode chips2to the outside when diode chips2are turned on by heavy current flowing through wiring conductors4and diode chips2. Each outer bare end surface of projections16in cutouts3ais flush with or slightly protrudes from outer surfaces of plastic encapsulant3.

Also, in the light emitting diode according to the present invention, semiconductor light emitting device can be mounted on a circuit board in the horizontal mounting structure (top view) as shown inFIGS. 4 and 5to emit light from light emitting elements2vertically to circuit board while bottom surface14of support plate1and lead ends4dof wiring conductors4are connected to corresponding areas on circuit board, but in another aspect, the device also can be mounted on circuit board in the vertical mounting structure (side view) as shown inFIGS. 6 and 7to emit light from light emitting element2horizontally and parallel with circuit board while projections16of support plate1and lead ends4dof wiring conductors4are connected to corresponding areas on circuit board. As wiring conductors4are attached on upper surface13and long side surfaces12aof support plate1through insulator6and are sealed by plastic encapsulant3, wiring conductors4do not bar the connection between projections16of support plate1and circuit board to firmly achieve the vertical mounting of semiconductor light emitting device. In the horizontal or vertical mounting structure, bottom surface14or projections16of support plate1and lead ends4dof wiring conductors4are securely connected to circuit board via solder or electrically conductive adhesive. Contact area of each projection16to circuit board is determined to an extent capable of providing the preferable connection between projections16and circuit board and the better heat radiation property through projections16.

Plastic encapsulant3has vertical planar surfaces15generally perpendicularly to support surface13aof support plate1, and each vertical surface15is formed with cutouts3aat the middle of long side surfaces12aof support plate1, and bottom slots3bextending along bottom surface14of support plate1for defining an end surface3cof plastic encapsulant3, and lead ends4dof wiring conductors4extend outwardly through bottom slots3b. As shown inFIGS. 1 and 5, bottom slot3bis formed between a wide projection16aformed at the center of long side surface12aand a pair of narrow protrusions16bformed at the opposite ends of long side surface12aso that wiring conductors4is folded along end surface3caway from support plate1. In this way, projections16are exposed in cutouts3awith bare end surface of projections16generally or substantially flash or coplanar with planar surfaces15, and lead ends4dof wiring conductors4are extended outwardly through bottom slots3bto provide the vertical mounting structure wherein the semiconductor light emitting device is attached on circuit board while planar surface15of plastic encapsulant3confronts or comes into contact to circuit board to electrically connect projection16of support plate1and shorter lead ends4dof wiring conductors4to circuit board. Otherwise, the semiconductor light emitting device can be mounted on circuit board in the horizontal mounting structure while wiring conductors4can be folded in bottom slot3away from bottom surface14of support plate1to allow bottom surface14of support plate1to directly be in contact to circuit board without interference by wiring conductors4.

Each of light emitting diode chips2according to the present invention comprises an anode or upper electrode2aelectrically connected to junction terminal4cof wiring conductor4through lead wire8, and a cathode or bottom electrode2belectrically connected to support surface13aof support plate1. In the horizontal mounting structure of light emitting diode device, bottom electrode2bof semiconductor light emitting element2is electrically connected to circuit board through bottom surface14of support plate1so that electric current flows from upper electrode2athrough light emitting diode2, bottom electrode2band bottom surface14to circuit board. In the vertical mounting structure of light emitting diode device, electric current flows from upper electrode2athrough light emitting diode2, bottom electrode2band projection16to circuit board. As shown inFIG. 5, left and right wiring conductors4aand4bare secured to support plate1symmetrically or in mirror image to attach both of wiring conductors4aand4bon circuit board for stable and firm mounting of the diode device on circuit board, but the only left wiring conductor4acan selectively be electrically connected to upper electrode2aof diode chip2through lead wire8. Accordingly, upper or bottom electrode2aor2bof diode chip2may be electrically connected to right wiring conductor4b. Stable and firm mounting of the diode device prevents deviation or deflection in optical axis of light emitting diode chip2. However, in the vertical mounting structure, wiring conductor4bnot connected to electrode of light emitting diode chip2may be removed. As shown inFIGS. 2 and 5, junction terminal4cof wiring conductor4is formed into a wider area than the remaining portion to form a bonding pad to which one end of lead wire8is connected. As mentioned above, bonding pad formed by junction terminal4cof wiring conductor4is mounted on upper surface13of support plate1via insulator6out of plastic encapsulant3which covers a portion of upper surface13of support plate1.

In manufacturing light emitting diode device shown inFIGS. 1 to 7, a plurality of wiring conductors4are simultaneously formed as a leadframe from a metallic strip utilizing a well-known pressing technique which provides wiring conductors4extending from one side of connectors19as shown inFIG. 8. Formed by a similar pressing technique as that for wiring conductors4is support plate1which comprises upper surface13and long side surface12aon which insulating tapes are attached to provide insulators6, and wiring conductors4are disposed after folded to form bent portion4e. In lieu of tapes, liquid insulating resin may be applied on upper surface13and long side surface12aof support plate1, and wiring conductors4are mounted on insulating resin to electrically insulate wiring conductors4from support plate1. Also, insulator6may be formed of the same material as that of plastic encapsulant3.

Then, plastic encapsulant3is formed on support plate1utilizing a well-known injection molding technique to seal upper surface13, long and short side surfaces12of support plate1and wiring conductors4by plastic encapsulant3. Before or after molding plastic encapsulant3on support plate1, light emitting diodes2are bonded on support surfaces13aof support plate1by means of well-known die bonder, and then, upper electrodes2aof diode chips2are electrically connected to junction ends4cof wiring conductors4utilizing well-known wire bonding technique. Subsequently, protective resin5is filled in hole1adefined by inclined surfaces1bof support plate1and inclined and vertical surfaces3dand3eof plastic encapsulant3by means of well-known dispenser. Finally, disused portions such as connectors19are removed from leadframe to finish a complete light emitting diode shown inFIGS. 1 to 7.

Embodiments of the semiconductor light emitting diode device according to the present invention can be further varied in various ways without limitation to the foregoing embodiments. For example, insulators6may be extended from upper surface13through long side surface12ato bottom surface14of support plate1. Also, as shown inFIG. 10, dents12cmay be formed on long side surface12aalong bottom surface14of support plate1. These extended insulators6and dents12cpromote better electric insulation between support plate1and wiring conductors4. Moreover, as shown inFIG. 11, light emitting diode2may comprise anode and cathode electrodes2aand2bon the upper surface to electrically connect junction terminal4cof left and right wiring conductors4aand4bto anode and cathode electrodes2aand2b.

While the foregoing embodiments exhibit light emitting diode devices provided with eight light emitting diode chips2, and sixteen wiring conductors4located on the opposite sides of diode chips2, however, the number, arrangement and configuration of diode chips2and wiring conductors4may be determined as required, and diode chips2may be selected for example from the group of blue, red and green or any single color or combined color light emitting diodes. Also, support plate1comprises three protrusions16aand16bon long side surface12a, however, the number and shape of these protrusions16aand16bmay be modified as demanded to conform to shape or requirement of light emitting diode device. Further, short side surface12bmay comprise any projection to more improve the heat radiation property of support plate1.

As mentioned above, the present invention can discharge heat from semiconductor light emitting element to the outside through projections of support plate extending through cutouts for outward exposure when light emitting element is illuminated with heavy current passing therethrough. Also, the semiconductor light emitting device can selectively or securely be mounted on circuit board in the horizontal or vertical mounting structure with bottom surface or projection of support plate in contact to or in face of circuit board.