Abstract:
A semiconductor light emitting device of what is called a side view type can achieve directional characteristics having substantial symmetry with respect to an optical axis. The semiconductor light emitting device can emit light in a direction substantially parallel to a surface on which the semiconductor light emitting device is to be held. The semiconductor light emitting device can include a semiconductor light emitting element emitting light in a light emitting direction parallel to the surface on which the semiconductor light emitting element is to be held, a base substrate having a main surface on which the semiconductor light emitting device is held, the main surface being parallel to the surface on which the semiconductor light emitting device is to be held. The base substrate can have a cutoff portion defined forward of the semiconductor light emitting element in the light emitting direction and in a position in which light emitted from the semiconductor light emitting element crosses the main surface. A light-transmitting first sealing resin can be provided on the base substrate, to bury the semiconductor light emitting element while filling the cutoff portion. The light emitted from the semiconductor light emitting element can travel through the cutoff portion.

Description:
This application claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2009-070006 filed on Mar. 23, 2009, which is hereby incorporated in its entirety by reference. 
     BACKGROUND 
     1. Technical Field 
     The presently disclosed subject matter relates to a semiconductor light emitting device. In particular, the presently disclosed subject matter relates to a semiconductor light emitting device of what is called a side view type for emitting light mainly in a direction substantially parallel to a surface on which the semiconductor light emitting device is to be held. 
     2. Related Art 
     Backlight units used in a liquid crystal display device may include backlight units of both an edge light type and those of a direct type. Thin liquid crystal display devices incorporated in cell phones, notebook personal computers, and other devices generally employ the edge light type backlight unit. According to the edge light type backlight unit, light emitted from a light source enters a light-transmitting light guide plate through a side surface of the light guide plate. Then, the traveling direction of the light is changed by using reflection dots and the like provided on a surface of the light guide plate, so that the whole surface of the light guide plate is uniformly illuminated. This surface light emission constitutes backlight units of liquid crystal display devices. 
     Light sources for use in the edge light type backlight unit include light emitting diodes (LEDs) for compact liquid crystal display devices such as those used in cell phones, as well as cold-cathode tubes (CCLFs). LEDs for use in the edge light type backlight unit can be what are called side view type LEDs each having a light emitting surface extending in a direction substantially perpendicular to a surface on which an LED package is mounted. 
       FIG. 1  shows an exemplary structure of a conventional side view type semiconductor light emitting device. The conventional side view type semiconductor light emitting device can include a first substrate  100  with electrodes formed on its surface, an LED chip  110  mounted on the first substrate  100 , a spacer  120  provided on the first substrate  100 , a second substrate  130  facing the first substrate  100  with the spacer  120  interposed therebetween, and a light-transmitting resin  140  applied to fill a space defined by the first and second substrates  100  and  130  and by the spacer  120 , the light-transmitting resin  140  burying the LED chip  110 . (See, for example, Japanese Patent Application Laid-Open No. 2007-59612.) 
     The semiconductor light emitting device of the conventional structure has suffered from the deviation of directional characteristics of light emitted from a light emitting surface  300 .  FIG. 2  shows directional characteristics of the conventional side view type semiconductor light emitting device described above, and describes the proportion of light intensity as viewed in an angle range of θ degrees with respect to a light source when the axial light intensity is 100%. As shown in  FIG. 2 , light emitted from the light source does not spread symmetrically in a horizontal direction (or optical axis). Rather, the intensity of the light tends to decrease in a region below a surface on which the LED chip  110  is mounted (in a region closer to a surface  200  on which the semiconductor light emitting device is to be held), and tends to increase in a region above that surface. This is because light emitted from the LED chip  110  toward the surface  200  is reflected off a surface of the first substrate  100  as shown in  FIG. 1 . These directional characteristics of light reduces efficiency of light entry into a light guide plate, by which nonuniformity of brightness may be generated in the surface of the light guide plate. 
     SUMMARY 
     The presently disclosed subject matter was devised in view of these and other characteristics, features, and problems and in association with the conventional art. According to an aspect of the presently disclosed subject matter, there can be provided a semiconductor light emitting device of what is called a side view type that achieves directional characteristics having improved or substantial symmetry with respect to an optical axis. 
     According to another aspect of the presently disclosed subject matter, a semiconductor light emitting device can emit light in a direction substantially parallel to a surface on which the semiconductor light emitting device is to be held, and the semiconductor light emitting device can include: a semiconductor light emitting element configured to emit light in a light emitting direction parallel to the surface on which the semiconductor light emitting element is to be held; a base substrate having a main surface on which the semiconductor light emitting device is held, the main surface being parallel to the surface on which the semiconductor light emitting device is to be held, the base substrate having a cutoff portion defined forward of the semiconductor light emitting element in the light emitting direction, the cutoff portion being defined in a position in which light emitted from the semiconductor light emitting element crosses the main surface; and a light-transmitting first sealing resin provided on the base substrate, the first sealing resin configured to bury the semiconductor light emitting element while filling the cutoff portion, wherein light emitted from the semiconductor light emitting element can travel through the cutoff portion. 
     In the above aspect of the presently disclosed subject matter, the cutoff portion can penetrate the base substrate. 
     In the above aspect of the presently disclosed subject matter, the cutoff portion can have a length longer than one side of the semiconductor light emitting element. 
     In the above aspect of the presently disclosed subject matter, the semiconductor light emitting device can have an end face in the light emitting direction serving as a light emitting surface, and the semiconductor light emitting element can be disposed on a center axis of a light emitting region at the light emitting surface. 
     In the above aspect of the presently disclosed subject matter, the first sealing resin can include a wavelength conversion material. 
     In the above aspect of the presently disclosed subject matter, the first sealing resin can include a light scattering material. 
     In the above aspect of the presently disclosed subject matter, the semiconductor light emitting device can further include a second sealing resin provided on or adjacent to the first sealing resin. 
     In the above aspect of the presently disclosed subject matter, the second sealing resin can have a light reflectance property. 
     According to still another aspect of the presently disclosed subject matter, a semiconductor light emitting device can emit light in a direction substantially parallel to a surface on which the semiconductor light emitting device is to be held, and the semiconductor light emitting device can include: a semiconductor light emitting element configured to emit light in a light emitting direction parallel to the surface on which the semiconductor light emitting device is to be held; a base substrate having a top surface on which the semiconductor light emitting element is mounted, and a back surface serving as the surface on which the semiconductor light emitting device is to be held; a first sealing resin configured to seal the semiconductor light emitting element; a spacer member provided to partially surround the first sealing resin; a second sealing resin configured to cover the semiconductor light emitting element, the first sealing resin and the spacer member from above; and a light emitting surface defined by the base substrate, the spacer member and the second sealing resin, the light emitting surface extending in a direction substantially perpendicular to the surface on which the semiconductor light emitting device is to be held, wherein a cutoff portion is defined in part of an edge of the base substrate, the edge defining the light emitting surface. 
     According to still another aspect of the presently disclosed subject matter, a method for manufacturing the semiconductor light emitting device of the presently disclosed subject matter, can include: preparing a die pad, and a base substrate having a cutoff portion defined close to the die pad; mounting a semiconductor light emitting element onto the die pad; fixedly providing a spacer on the base substrate to surround the semiconductor light emitting element; applying a light-transmitting resin to fill a space around the semiconductor light emitting element; fixedly providing a frame member on the spacer; and applying a sealing resin to fill a space surrounded by the frame member, the light-transmitting resin, and the spacer. 
     The semiconductor light emitting device of the presently disclosed subject matter can achieve directional characteristics having improved or substantial symmetry in an angle range of θ degrees with respect to an optical axis as a center. Accordingly, the semiconductor light emitting device of the presently disclosed subject matter is suitably adopted for use with a light guide plate and the like for constituting a backlight unit of a liquid crystal display device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other characteristics, features, and advantages of the presently disclosed subject matter will become clear from the following description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a cross sectional view illustrating the structure of a conventional side view type semiconductor light emitting device; 
         FIG. 2  is a graph showing the directional characteristics of the conventional side view type semiconductor light emitting device; 
         FIG. 3  is a top view of a semiconductor light emitting device made in accordance with principles of the presently disclosed subject matter; 
         FIG. 4  is a cross sectional view taken along a line  4 - 4  shown in  FIG. 3 ; 
         FIG. 5  is a cross sectional view taken along a line  5 - 5  shown in  FIG. 3 ; 
         FIG. 6  is a cross sectional view of a semiconductor light emitting device according to another exemplary embodiment of the presently disclosed subject matter; 
         FIG. 7  is a perspective exploded view illustrating the structure of a backlight unit for use in a liquid crystal display device, the backlight unit employing an embodiment of a semiconductor light emitting device of the presently disclosed subject matter as a light source; 
         FIGS. 8A to 8D  are top views of semiconductor light emitting devices in processes of manufacture according to one exemplary embodiment of the presently disclosed subject matter; 
         FIGS. 9E to 9G  are top views of semiconductor light emitting devices in processes of manufacture according to the exemplary embodiment of the presently disclosed subject matter of  FIGS. 8A-8D ; 
         FIG. 10A  is a top view illustrating a first resin substrate with a plurality of base substrates; 
         FIG. 10B  is a top view illustrating a second resin substrate with a plurality of spacer members; and 
         FIG. 10C  is a top view illustrating a third resin substrate with a plurality of frame members. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An exemplary embodiment of the presently disclosed subject matter will be described next with reference to drawings.  FIGS. 3 to 5  show the structure of a semiconductor light emitting device  1  according to an exemplary embodiment of the presently disclosed subject matter with  FIG. 3  being a top view,  FIG. 4  being a cross sectional view taken along line  4 - 4  shown in  FIG. 3 , and  FIG. 5  being a cross sectional view taken along line  5 - 5  shown in  FIG. 3 . In order to clearly show the structure of the semiconductor light emitting device  1  as viewed from above, first and second sealing resins  50  and  60  are not shown in  FIG. 3 . 
     The semiconductor light emitting device  1  of the exemplary embodiment can include an LED chip  10  that serves mainly as a light emitting element and a base substrate  20  on which the LED chip  10  is mounted. A second sealing resin  60  can be applied to cover the LED chip  10  from above to seal the LED chip  10  and other structures. Frame members  40  can be configured to define a region in which the second sealing resin  60  is to be applied. A spacer member  30  can be configured to define a space between the base substrate  20  and the second sealing resin  60 , and a light-transmitting first sealing resin  50  can be applied to fill the space. 
     The LED chip  10  serving as a light emitting element can be a blue LED made, for example, of a GaN semiconductor, and can have a stacked structure of semiconductor films including an n-layer, a light emitting layer, and a p-layer, for example (each of which is not shown). An anode electrode and a cathode electrode (not shown) can be formed on the upper surface of the LED chip  10 . An exemplary size and an exemplary thickness of the LED chip  10  can be 0.3 mm×0.3 mm, and 0.1 mm, respectively. The LED chip  10  may be mounted by soldering or a joining process using an adhesive or the like onto a die pad  21  formed on the base substrate  20 . It should be noted that the LED chip  10  as described above can be utilized for a side view type semiconductor light emitting device, and accordingly, can have a light emitting direction sidewards with respect to the stacked surfaces. 
     The base substrate  20  can be formed by a base material made of, for example, a glass epoxy resin and a conductive pattern formed on a surface of the base material, the conductive pattern can be made of Cu foil or the like. Definition of the conductive pattern can form the die pad  21  in the central part of the base substrate  20 , and bonding pads  22  on opposite sides of the die pad  21 . The anode electrode and the cathode electrode on the upper surface of the LED chip  10  can be electrically connected through bonding wires  11  to the bonding pads  22 . The back surface of the base substrate  20  can serve as a surface  70  on which the semiconductor light emitting device  1  is to be held when the semiconductor light emitting device  1  is mounted to a circuit board. The surface  70  can include back interconnects  23  formed thereon that are electrically connected by through holes (not shown) to the corresponding bonding pads  22 . The back interconnects  23  can constitute junction parts when the semiconductor light emitting device  1  is mounted to the circuit board. 
     The base substrate  20  can have a cutoff portion  90  defined on the side of a light emitting surface  80  of the semiconductor light emitting device  1 , namely defined forward of the LED chip  10  in a light emitting direction (out of the paper, as shown in  FIG. 3 ). The cutoff portion  90  can be greater in length in a direction in which the cutoff portion  90  extends than the length of one side of the LED chip  10  (in the left-to-right direction in  FIG. 3 ). 
     The spacer member  30  can be provided on the base substrate  20  in order to define a space between the base substrate  20  and the second sealing resin  60 . The spacer member  30  can have a cutoff portion  31  that is substantially semicircular in top view as shown in  FIG. 3 . The spacer member  30  can be formed so that the LED chip  10  is located in the center of the cutoff portion  31 . That is, the LED chip  10  may be surrounded by the spacer member  30  with an opening exposed to the light emitting surface  80 . Like that of the base substrate  20 , the base material for the spacer member  30  may be a glass epoxy resin. The spacer member  30  may be joined with the base substrate  20  by a commercially available adhesive sheet, for example. In light of clearance to be defined between the loop top portions of the bonding wires  11  and the second sealing resin  60 , the thickness of the spacer member  30  may be set to about 0.2 mm, for example. A light reflection member such as a metal film may be arranged on the inner wall of the semicircular cutoff portion  31  of the spacer member  30 . Furthermore, a material having light reflectivity such as alumina may be used as the base material of the spacer member  30 . 
     The light-transmitting first sealing resin  50  made of a silicone resin or the like can be applied to fill a space defined on the base substrate  20  and surrounded by the spacer member  30 . In this way, the LED chip  10  and the bonding wires  11  can be buried in the first sealing resin  50 . The cutoff portion  90  can also be filled with the first sealing resin  50  as shown in  FIG. 5 . A wavelength conversion material such as a fluorescent substance may be dispersed in the first sealing resin  50 . The wavelength conversion material employed herein may be a YAG:Ce fluorescent substance that is made by doping Ce (cerium) as an activator into YAG. The wavelength conversion material can absorb blue light with a peak wavelength of about 460 nm emitted from the LED chip  10 , and converts the absorbed light to yellow light with a peak wavelength of about 560 nm. Then, the yellow light emitted from the wavelength conversion material and the blue light that passes through the first sealing resin  50  without being subjected to wavelength conversion are mixed together, so that white light is obtained from the light emitting surface  80 . The first sealing resin  50  may also contain a light scattering material, such as silica or diamond particles, with a particle diameter of 1 to 5 μm. 
     Provided on the spacer member  30  are the frame members  40  as a pair that are arranged to extend along opposite side edge surfaces of the semiconductor light emitting device  1 . The frame members  40  may be made of, for example, a glass epoxy resin. The frame members  40  may be joined with the spacer member  30  by a commercially available adhesive sheet. The second sealing resin  60  can be applied to fill the space defined between the two frame members  40  defining the space therebetween. The second sealing resin  60  can cover the first sealing resin  50  that can seal the LED chip  10 , the bonding wires  11  and other structures. The second sealing resin  60  can also serve to prevent leakage of light from surfaces other than the light emitting surface  80 . Thus, a resin material exhibiting excellence in light reflectivity can be used as a material of the second sealing resin  60 . As an example, the second sealing resin  60  may be made by mixing titanium oxide power into a light-transmitting resin such as a silicone resin or the like. In this way, the LED chip  10  can be surrounded by a material of high reflectivity, by which efficiency of light extraction from the light emitting surface  80  is improved. 
     In the thus configured semiconductor light emitting device  1 , the cutoff portion  90  can be defined in the base substrate  20 . In this way, as shown in  FIG. 5 , the structure of the semiconductor light emitting device  1  does not have a region, in which light emitted from the LED chip  10  may be intercepted, forward of the LED chip  10  in the light emitting direction. This can place the LED chip  10  in the center of a light emitting region on the light emitting surface  80 . In more detail, light emitted from the LED chip  10  can pass through the cutoff portion  90 , and then exit from the light emitting surface  80  without being intercepted by the base substrate  20 . Accordingly, light traveling from the LED chip  10  toward the surface  70  can be directly extracted. This can form uniform distribution of light intensity in an angle range of θ degrees with respect to the LED chip  10  as a center. Accordingly, applying the semiconductor light emitting device  1  of the presently disclosed subject matter as a light source of a backlight unit of a liquid crystal display panel can achieve substantially uniform emission of light from the main surface of a light guide plate. Furthermore, the cutoff portion  90  can be filled with the first sealing resin  50  containing a light scattering material. This can cause scattering of light passing through the cutoff portion  90 , by which favorable directional characteristics can be obtained. 
     While the cutoff portion  90  can penetrate the base substrate  20  as shown in  FIG. 5 , an alternative formation of the cutoff portion  90  shown in  FIG. 6  may be configured such that the base substrate  20  remains on its lower surface side. The shape and the dimension of the cutoff portion  90 , and a region in which the cutoff portion  90  is to be defined, may suitably be changed as long as these changes achieve desirable directional characteristics. 
     Instead of the second sealing resin  60 , a plate member such as a resin substrate or a ceramic substrate arranged so as to face the base substrate  20  with the spacer member  30  interposed therebetween may be provided to cover the upper surface of the semiconductor light emitting device  1 . In this case, the plate member can be made of a material with high reflectivity at least regarding a surface contacting the first sealing resin  50 . 
     The present exemplary embodiment includes only one light emitting surface. Alternatively, two or more surfaces that cross the surface  70  may serve as light emitting surfaces. 
       FIG. 7  is a perspective view of the structure of a backlight unit for use in a liquid crystal display device, and which employs an example of a semiconductor light emitting device  1  of the presently disclosed subject matter as a light source. The illustrated backlight unit can include light guide plate  500 , a reflection sheet  510  provided backward of the light guide plate  500 , a diffusion sheet  520  and a prism sheet  530  that are provided forward of the light guide plate  500 , and a plurality of semiconductor light emitting devices  1  that are attached to one edge surface of the light guide plate  500 . Light beams emitted from the semiconductor light emitting devices  1  can spread throughout the light guide plate  500 . The reflection sheet  510  can reflect light from the light guide plate  500  forward (left-downward direction in  FIG. 7 ). The diffusion sheet  520  can improve nonuniformity of intensity of light emitted from the light guide plate  500 . The prism sheet  530  can provide homogeneity of intensity of light entering the prism sheet  530  from the diffusion sheet  520 , and can guide the light to a liquid crystal display device arranged forward of the prism sheet  530 . 
     Next, an exemplary method for manufacturing semiconductor light emitting devices  1  of the exemplary embodiment will be described with reference to  FIGS. 8A to 8D ,  FIGS. 9E to 9G , and  FIGS. 10A to 10C .  FIGS. 8A to 8D  and  FIGS. 9E to 9G  are top views of the semiconductor light emitting device  1  in processes of manufacture.  FIG. 10A  shows a first resin substrate  25  with a plurality of base substrates  20  used to manufacture the semiconductor light emitting devices  1 .  FIG. 10B  shows a second resin substrate  35  with a plurality of spacer members  30 .  FIG. 10C  shows a third resin substrate  45  with a plurality of frame members  40 . In the present exemplary embodiment, a plurality of semiconductor light emitting devices  1  can be manufactured simultaneously by using the resin substrates  25 ,  35  and  45 .  FIGS. 8A to 8D  and  FIGS. 9E to 9G  each show only four of the semiconductor light emitting devices  1  to be manufactured together. 
     First, the first resin substrate  25  is prepared. The first resin substrate  25  can include the plurality of integrally formed base substrates  20  arranged in a matrix ( FIGS. 8A and 10A ). Each of the base substrates  20  in the first resin substrate  25  can have the die pad  21  provided in the central part of the base substrate  20 . The bonding pads  22  can be provided on opposite sides of the die pad  21 . The bonding pads  22  can be electrically connected by through holes  24  to the back interconnects  23 . A penetration hole for forming the cutoff portion  90  can be defined in each of the die pads  21 . In  FIG. 10A , the die pads  21 , the bonding pads  22  and the cutoff portion  90  are not shown, and a boundary between adjacent ones of the base substrates  20  is indicated by dashed lines. 
     Next, an adhesive can be applied by a dispensing process onto the die pad  21  of each of the base substrates  20 . Then, the LED chip  10  can be mounted on the die pad  21 , and the applied adhesive can be cured. An anode electrode and a cathode electrode formed on the top surface of each of the LED chips  10  can be connected by the bonding wires  11  to the bonding pads  22  ( FIG. 8B ). Herein, it is assumed that the LED chips  10  are each a back electrode type LED chip with an anode electrode or a cathode electrode provided on its back surface. In this case, the conductive pattern of the base substrates  20  can suitably be changed in order to supply power to the LED chips  10  through the respective back interconnects  23  and the respective die pads  21 . Also in this case, each of the LED chips  10  and the corresponding base substrate  20  can be joined by a conductive bonding agent such as an Ag paste or solder. Furthermore, the number of bonding wires (or other bonding structures) required is one. 
     The second resin substrate  35  can be prepared next. The second resin substrate  35  can include the plurality of integrally formed spacer members  30  arranged in a matrix as shown in  FIG. 10B . A plurality of penetration holes  31   a  for forming the semicircular cutoff portions  31  of the spacer members  30  can be defined in the second resin substrate  35 . In  FIG. 10B , a boundary between adjacent ones of the spacer members  30  is indicated by dashed lines. 
     The first resin substrate  25  with the LED chips  10  mounted thereon and the second resin substrate  35  can thereafter be bonded by an adhesive sheet or the like. The bonding of the second resin substrate  35  to the first resin substrate  25  can be achieved such that two adjacent ones of the LED chips  10  mounted on the base substrates  20  and the bonding wires  11  belonging to the same base substrates  20  are exposed through the penetration holes  31   a  ( FIG. 8C ). 
     Then, the first sealing resin  50  made of a silicone resin or the like can be applied by a process such as dispensing so as to bury the LED chips  10  and the bonding wires  11  in the penetration holes  31   a . The application of the first sealing resin  50  can be carried out such that the upper surface of the applied first sealing resin  50  has a height substantially the same as that of the upper surfaces of the spacer members  30 . The applied first sealing resin  50  may be slightly greater in thickness at a portion above each of the LED chips  10  on the corresponding base substrate  20  than at other portions on the same base substrate  20 , so that the applied first sealing resin  50  will be in the form of a convex in each of the base substrates  20  ( FIG. 8D ). This can increase the area of a light emitting surface near an optical axis, thereby improving efficiency of light extraction. Next, as shown in  FIG. 10C , the third resin substrate  45  of a thickness of about 150 μm and with a plurality of pairs of frame members  40  can be prepared. A plurality of penetration slots  41  for making the frame members  40  as a pair apart from each other can be defined in the third resin substrate  45 . In  FIG. 10C , a boundary between the frame members  40  belonging to adjacent pairs is indicated by dashed lines. The second resin substrate  35  and the third resin substrate  45  can be thereafter bonded by an adhesive sheet or the like. The bonding of the third resin substrate  45  can be carried out such that each of the penetration holes  31   a  filled with the first sealing resin  50  is completely exposed in the corresponding penetration slot  41 . As a result, the frame members  40  as a pair can be arranged on opposite side edge surfaces of each of the semiconductor light emitting devices  1 , and a concave space with a bottom part defined by surfaces of the spacer member  30  and the first sealing resin  50  can be formed in each of the semiconductor light emitting devices  1  ( FIG. 9E ). 
     Next, the second sealing resin  60  made by mixing titanium oxide powder into a silicone resin can be applied by a process such as dispensing to fill the concave spaces formed between the frame members  40  in pairs. The application of the second sealing resin  60  can be carried out such that the upper surface of the applied second sealing resin  60  has a height that is substantially the same as that of the upper surface of the frame members  40 . Further, the loop top portions of the bonding wires  11  projecting from the surface of the applied first sealing resin  50  can be buried in the second sealing resin  60  ( FIG. 9F ). 
     Then, the second sealing resin  60  can be cured, and the structure obtained by following the above-described steps can be diced into the plurality of individual semiconductor light emitting devices  1  ( FIG. 9G ) to complete the manufacture of the semiconductor light emitting devices  1 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed subject matter without departing from the spirit or scope of the presently disclosed subject matter. Thus, it is intended that the presently disclosed subject matter cover the modifications and variations of the presently disclosed subject matter provided they come within the scope of the appended claims and their equivalents. All related art references described above are hereby incorporated in their entirety by reference.