[0001]This application is a Continuation of U.S. Ser. No. 12/668,554, filed Jan. 11, 2010, which is a National Stage Application of PCT/JP2008/062313, filed Jul. 8, 2008, which applications are incorporated herein by reference.
[0002]TECHNICAL FIELD
[0003]The present invention relates to a light emitting device including a plurality of semiconductor light emitting elements, in particular, to a side-view type light emitting device.
[0004]BACKGROUND ART
[0005]FIG. 4 illustrates an example of a conventional semiconductor light emitting device (see Patent Document 1 identified below, for example). The semiconductor light emitting device X illustrated in the figure includes a substrate 91 and three semiconductor light emitting elements 93 R, 93 G, 93 B mounted on the main surface of the substrate 91 . Specifically, the substrate 91 is provided with electrodes 92 R, 92 G, 92 B on which the semiconductor light emitting elements 92 R, 92 G, 92 B are bonded, respectively. The substrate 91 is further provided with a common electrode 92 C, to which the semiconductor light emitting elements 93 R, 93 G, 93 B are electrically connected via wires. The semiconductor light emitting elements 93 R, 93 G, 93 B are surrounded by a case 95 made of a resin. The semiconductor light emitting device X is designed as a side-view type light emitting device to be mounted on e.g. a printed circuit board with a longitudinal side surface of the substrate 91 utilized as the mount surface.
[0006]Patent Document 1: JP-A-2006-24794
[0007]In recent years, there is a demand for size reduction of semiconductor light emitting devices. As to the side-view type semiconductor light emitting device described above, it is demanded to reduce the projecting amount (i.e., height) of the light emitting device from the printed circuit board on which the light emitting device is mounted. However, the reduction of the projecting amount means the reduction of the area of the main surface of the substrate 91 , i.e., the reduction of the space required for placing the semiconductor light emitting elements 93 R, 93 G, 93 B and the wires connected to the light emitting elements. Generally, as the space becomes narrower, it becomes more technically difficult to arrange necessary circuits in the space. Thus, with the conventional structure of the semiconductor light emitting device X, there is a limit on the size reduction.
[0008]DISCLOSURE OF THE INVENTION
[0009]The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide a semiconductor light emitting device suitable for size reduction.
[0010]A semiconductor light emitting device provided according to the present invention includes an elongated substrate, a first, a second and a third semiconductor light emitting elements, and an electrode. The substrate has a main surface in the form of an elongated rectangle, a reverse surface opposite to the main surface, a mount surface extending between the main surface and the reverse surface. The substrate has a first end and a second end spaced from each other in the longitudinal direction of the substrate. The substrate is formed with a through-hole extending from the main surface to the reverse surface. The first, the second and the third light emitting elements are mounted on the main surface of the substrate. The electrode is electrically connected to the first semiconductor light emitting element and extends to the reverse surface of the substrate via the through-hole. The first semiconductor light emitting element and the through-hole are positioned between the second semiconductor light emitting element and the third semiconductor light emitting element in the longitudinal direction of the substrate. The second semiconductor light emitting element is arranged closer to the first end of the substrate, whereas the third semiconductor light emitting element is arranged closer to the second end of the substrate.
[0011]Preferably, the semiconductor light emitting device further includes a wire, and a pad formed on the main surface of the substrate. The wire has a first end bonded to the first semiconductor light emitting element and a second end bonded to the pad. The pad is arranged at a position deviated from the second semiconductor light emitting element toward the first end of the substrate in the longitudinal direction of the substrate.
[0012]Preferably, the semiconductor light emitting device of the present invention further includes an additional wire for connecting the second semiconductor light emitting element and the pad to each other.
[0013]Preferably, the main surface of the substrate has a side edge extending in the longitudinal direction of the substrate, and the first semiconductor light emitting element is positioned closer to the side edge than the second and the third semiconductor light emitting elements are.
[0014]Preferably, the first semiconductor light emitting element is smaller in size than the second and the third semiconductor light emitting elements.
[0015]Preferably, the first semiconductor light emitting element is adapted to emit red light. One of the second and the third semiconductor light emitting elements is adapted to emit blue light, whereas the other one of the second and the third semiconductor light emitting elements is adapted to emit green light.
[0016]Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.
[0017]BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view illustrating an example of a semiconductor light emitting device according to the present invention. FIG. 2 is a rear view illustrating the semiconductor light emitting device of FIG. 1 . FIG. 3 is a sectional view taken along lines in FIG. 1 . FIG. 4 is a plan view illustrating an example of a conventional semiconductor light emitting device.
[0018]BEST MODE FOR CARRYING OUT THE INVENTION
[0019]A preferred embodiment of the present invention is described below with reference to the accompanying drawings.
[0020]FIGS. 1-3 illustrate an example of a semiconductor light emitting device according to the present invention. The illustrated light emitting device A includes an elongated insulating substrate 1 , electrodes 2 R, 2 G, 2 B, 2 C, semiconductor light emitting elements 3 R, 3 G, 3 B, wires 4 R, 4 G, 4 B, a case 5 and a transparent protective resin 6 ( FIG. 3 ). The light emitting device A is designed as a side-view type light emitting device to be mounted with a longitudinal side surface 1 C of the substrate 1 (lower surface in FIGS. 1-3 ) utilized as the mount surface. The semiconductor light emitting elements 3 R, 3 G and 3 B are adapted to emit red light, green light and blue light, respectively, which are combined to emit white light. The light emitting device A has a length L of about 2.7 mm, a height H of about 0.5 mm and a width W of about 0.95 mm. For easier understanding, the illustration of the protective resin 6 is omitted in FIG. 1 .
[0021]The substrate 1 is made of e.g. a glass fiber-reinforced epoxy resin and in the form of an elongated rectangle. The substrate 1 includes a main surface 1 A on which the three semiconductor light emitting devices 3 R, 3 G, 3 B are mounted, and a reverse surface 1 B opposite to the main surface 1 A. The substrate 1 is formed with a through-hole 11 and a plurality of grooves 12 R, 12 G, 12 B, 12 C. As illustrated in FIG. 3 , the through-hole 11 extends from the main surface 1 A to the reverse surface 1 B of the substrate 1 (i.e., in the thickness direction of the substrate 1 ). The grooves 12 R, 12 B, 12 G, 12 C are provided in the mount surface 1 C of the substrate 1 (i.e., the lower surface in FIGS. 1-3 ) so as to be separated from each other and extend in the thickness direction of the substrate 1 . The substrate 1 has a length of about 2.7 mm, a height of about 0.5 mm and a width of about 0.5 mm. The through-hole 11 has an inner diameter of about 0.15 mm.
[0022]The electrodes 2 R, 2 G, 2 B, 2 C are made of a plating layer of Cu, Ni or Au, for example, and formed on the main surface 1 A, the side surface 1 C (mount surface) and the reverse surface 1 B of the substrate 1 . The electrodes 2 R, 2 G, 2 B, 2 C are utilized for supplying power to the semiconductor light emitting elements 2 R, 2 G, 2 B and mounting of the light emitting device A.
[0023]The electrode 2 R is connected to the semiconductor light emitting element 3 R and includes a bonding pad 2 Ra, a first annular portion 2 Rb, a cylindrical portion 2 Rc, a second annular portion 2 Rd, a strip portion 2 Re, a reverse surface portion 2 Rf and a mount portion 2 Rg. The bonding pad 2 Ra is provided on the main surface 1 A of the substrate 1 at the center in the longitudinal direction, and the semiconductor light emitting element 2 R is bonded to the bonding pad 2 Ra. In the illustrated example, the bonding pad 2 Ra is X-shaped. The first annular portion 2 Rb adjoins the bonding pad 2 Ra in the width direction of the substrate 1 (height direction) and surrounds the opening of the through-hole 11 on the main surface 1 A of the substrate 1 . The cylindrical portion 2 Rc (see FIG. 3 ) is formed to cover the inner surface of the through-hole 11 . The second annular portion 2 Rd surrounds the opening of the through-hole 11 on the reverse surface 1 B of the substrate 1 . As illustrated in FIG. 2 , the strip portion 2 Re extends from the annular portion 2 Rd toward an end of the substrate 1 in the longitudinal direction. The reverse surface portion 2 Rf is provided on the reverse surface 1 B of the substrate 1 to surround a corner. The reverse surface portion 2 Rf is utilized for promoting formation of a solder fillet in mounting the light emitting device A on a circuit board. The mount portion 2 Rg is formed to cover the wall surface of the groove 12 R and utilized for mounting of the light emitting device A.
[0024]The electrodes 2 B and 2 G serve to supply power to the semiconductor light emitting elements 2 B and 2 G and include bonding pads 2 Ba, 2 Ga, semi-annular portions 2 Bb, 2 Gb, mount portions 2 Bc, 2 Gc and reverse surface portions 2 Bd, 2 Gd, respectively. The bonding pads 2 Ba and 2 Ga, on which the semiconductor light emitting elements 3 B and 3 G are bonded, respectively, are arranged to be spaced from each other in the longitudinal direction of the substrate 1 so as to face toward each other across the through-hole 11 . In the illustrated example, the bonding pads 2 Ba, 2 Ga and the through-hole 11 are aligned in the longitudinal direction of the substrate 1 . The bonding pads 2 Ba and 2 Ga are X-shaped. The semi-annular portions 2 Bb, 2 Gb are arranged to reach a long side of the substrate 1 and surround the openings of the grooves 12 B and 12 G, respectively, on the main surface 1 A of the substrate 1 . The semi-annular portions 2 Bb, 2 Gb are provided at locations deviated from the bonding pads 2 Ba, 2 Ga toward the two ends of the substrate 1 in the longitudinal direction. The mount portions 2 Bc and 2 Gc are formed to cover the grooves 12 B and 12 G, respectively, and utilized for mounting of the light emitting device A. The reverse surface portions 2 Bd and 2 Gd surround the openings of the grooves 12 B and 12 G on the reverse surface 1 B of the substrate 1 , respectively, and are utilized for promoting formation of a solder fillet in mounting the light emitting device A.
[0025]The electrode 2 C is an anode common electrode electrically connected to the anode electrodes (not shown) of the semiconductor light emitting elements 3 R, 3 G, 3 B. The electrode 2 C includes two pads 2 Ca for wire connection (the right pad 2 Ca and the left pad 2 Ca in FIG. 1 ), a strip portion 2 Cb, an arcuate portion 2 Cc, a mount portion 2 Cd and a reverse surface portion 2 Ce. Wires 4 R and 4 G are bonded to the right pad 2 Ca, whereas a wire 2 B is bonded to the left pad 2 Ca. The two pads 2 Ca are spaced from each other in the longitudinal direction of the substrate 1 . In the illustrated example, the two pads 2 Ca are provided on the main surface 1 A of the substrate 1 at locations close to the upper flat surface 1 D (the surface opposite to the mount surface 1 C) of the substrate 1 . In the longitudinal direction of the substrate 1 , the left pad 2 Ca is provided at a location deviated from the bonding pad 2 Ba toward the left end of the substrate 1 , whereas the right pad 2 Ca is provided at a location deviated from the bonding pad 2 Ga toward the right end of the substrate 1 . That is, in the longitudinal direction of the substrate 1 , the left pad 2 Ca is positioned between the bonding pad 2 Ba and the left end of the substrate 1 , whereas the right pad 2 Ca is positioned between the bonding pad 2 Ga and the right end of the substrate 1 . The strip portion 2 Cb is formed along a long side and a short side of the main surface 1 A of the substrate 1 . Part of the strip portion 2 Cb (the part extending between two pads 2 Ca) connects the two pads 2 Ca to each other. The arcuate portion 2 Cc is formed to surround the opening of the groove 12 C on the main surface 1 A of the substrate 1 . The mount portion 2 Cd is formed to cover the groove 12 C of the substrate 1 and utilized for mounting of the light emitting device A. The reverse surface portion 2 Ce surrounds the opening of the groove 12 C on the reverse surface 1 B of the substrate 1 and is utilized for promoting formation of a solder fillet in mounting the light emitting device A.
[0026]The semiconductor light emitting elements 3 R, 3 G and 3 B are fixed to the bonding pads 2 Ra, 2 Ga and 2 Ba via e.g. conductive paste, respectively. As will be understood from FIG. 1 , the three semiconductor light emitting elements 3 R, 3 G, 3 B are at positions corresponding to the three vertices of a triangle. Specifically, the center of the semiconductor light emitting element 3 R is at a position corresponding to the vertex of an isosceles triangle, whereas the center of each of the semiconductor light emitting elements 3 B and 3 G is at a position corresponding to an end of the base of the isosceles triangle. Further, the respective centers of the semiconductor light emitting elements 3 B and 3 G are positioned on a hypothetical straight line extending in the longitudinal direction of the substrate 1 . The center of the semiconductor light emitting element 3 R is closer to a longitudinal edge (upper edge in FIG. 1 ) of the main surface 1 A of the substrate 1 than the centers of the semiconductor light emitting elements 3 B and 3 G are. The rectangular surface of the semiconductor light emitting element 3 R illustrated in FIG. 1 is a square having sides of about 0.15 mm. The rectangular surface of each of the semiconductor light emitting elements 3 G and 3 B similarly illustrated in FIG. 1 is a square having sides of about 0.2 to 0.3 mm. In this way, the semiconductor light emitting element 3 R, which is adapted to emit red light, is smaller in size than the other two semiconductor light emitting elements 3 G and 3 B.
[0027]The wires 4 R, 4 G, 4 B are made of e.g. gold (Au) and electrically connect the anode electrodes (not shown) of the semiconductor light emitting elements 3 R, 3 G, 3 B to the electrode 2 C. As illustrated in FIG. 1 , the left end of the wire 4 R is connected to the semiconductor light emitting element 3 R, whereas the right end of the wire 4 R is connected to the right pad 2 Ca. The connection point of the right end of the wire 4 R is on the right side of the semiconductor light emitting element 3 G in the longitudinal direction of the substrate 1 . The left end of the wire 4 G is connected to the semiconductor light emitting element 3 R, whereas the right end of the wire 4 G is connected to the right pad 2 Ca. That is, both of the wires 4 R and 4 G are connected to the right pad 2 Ca at their right ends. The left end of the wire 4 B is connected to the left pad 2 Ca, whereas the right end of the wire 4 B is connected to the semiconductor light emitting element 3 B.
[0028]The case 5 is a frame-shaped member made of e.g. a white resin and surrounds the semiconductor light emitting elements 3 R, 3 G, 3 B, as will be understood from FIGS. 1-3 . The protective resin 6 is made of a transparent resin which transmits light emitted from the semiconductor light emitting elements 3 R, 3 G, 3 B and fills the space surrounded by the case 5 . The protective resin 6 protects the semiconductor light emitting elements 3 R, 3 G, 3 B.
[0029]As illustrated in FIGS. 2 and 3 , the reverse surface 1 B of the substrate 1 is formed with a resist film 7 . The resist film 7 prevents unfavorable connection of the electrodes 2 R, 2 G, 2 B, 2 C via solder in the process of mounting the light emitting device A. The resist film 7 also serves to protect the strip portion 2 Re. The opening of the through-hole 11 is closed by the resist film 7 on the reverse surface 1 B. With this arrangement, liquid resin as the material of the protective resin 6 is prevented from leaking through the through-hole 11 . As illustrated in FIG. 2 , the resist film 7 has an asymmetric shape so that the mounting of the light emitting device A with wrong polarity is prevented.
[0030]The advantages of the light emitting device A are described below. In the above-described arrangement, of the electrode 2 R, only the bonding pad 2 Ra and the first annular portion 2 Rb are provided on the main surface 1 A of the substrate 1 , and the other portions are provided on the inner wall of the through-hole 11 or the reverse surface 1 B or the mount surface 1 C of the substrate 1 . In this arrangement, the electrode 2 R does not include a portion extending from the semiconductor light emitting element 3 R to the periphery of the substrate 1 . This is suitable for mounting the three semiconductor light emitting elements 3 R, 3 G, 3 B in the narrow region of the main surface 1 A of the substrate 1 . Further, by arranging the three semiconductor light emitting elements 3 R, 3 G, 3 B in a triangular shape, it is possible to position the semiconductor light emitting elements 3 G and 3 B close to the semiconductor light emitting element 3 R and also position the semiconductor light emitting elements 3 G and 3 B close to each other. Thus, the light emitted from the semiconductor light emitting elements 3 R, 3 G, 3 B is properly combined together, whereby ideal white light is obtained.
[0031]As noted above, an end of the wire 4 R bonded to the semiconductor light emitting element 3 R is bonded to the right pad 2 Ca at a position on the right side of the semiconductor light emitting element 3 G in the longitudinal direction of the substrate 1 . With this arrangement, it is not necessary to provide a space for bonding the wire 4 R within the triangular region surrounded by the three semiconductor light emitting elements 3 R, 3 G, 3 B, which holds true for the other two wires 4 G and 4 B. This is suitable for arranging the semiconductor light emitting elements 3 R, 3 G, 3 B close to each other. Moreover, bonding the two wires 4 R and 40 to the single pad 2 Ca occupies less space than preparing an individual pad for each of the wires 4 R and 40 .
[0032]The semiconductor light emitting element 3 R, which is positioned at the center in the longitudinal direction of the substrate 1 , is made smaller in size than the other two semiconductor light emitting element 3 G and 3 B, as noted above. This is suitable for arranging the semiconductor light emitting elements 3 R, 3 G, 3 B close to each other. Further, clear white light is obtained by sandwiching the semiconductor light emitting element 3 R for emitting red light between the semiconductor light emitting elements 3 R and 3 B for emitting green light and blue light.
[0033]The semiconductor light emitting element to be used in the present invention is not limited to the type designed to be bonded at the lower surface, with a wire bonded to the upper surface. For instance, use may be made of a semiconductor light emitting element of the type in which two wires are to be bonded to the upper surface. Alternatively, use may be made of a semiconductor light emitting element of the flip chip mounting type which does not use a wire.
