Abstract:
A light-emitting device includes a first light-emitting element, a second light-emitting element, a third light-emitting element placed between the first and second light-emitting elements, and a bonding wire passing directly over the third light-emitting element and connecting the first light-emitting element with the second light-emitting element.

Description:
The present application is based on Japanese patent application No.2014-063836 filed on Mar. 26, 2014, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a light-emitting device and a method of manufacturing the light-emitting device. 
     2. Description of the Related Art 
     A light-emitting device is known which has plural light-emitting elements connected to each other through a bonding wire (see e.g. JP-A-2013-118292). 
     SUMMARY OF THE INVENTION 
     In the light-emitting device disclosed in JP-A-2013-118292, if the space between the plural light-emitting elements decreases along with the downsizing of the light-emitting device, the length of the bonding wire also decreases. Thus, it is difficult to install the bonding wire and, furthermore, the bonding wire may be broken due to stress generated by the expansion of a sealing resin formed on the plural light-emitting elements. 
     It is an object of the invention to provide a light-emitting device that is constructed so as to allow the easy installation of the bonding wire and to prevent the breakage of the bonding wire even when the space between the plural light-emitting elements is narrowed, as well as a method of manufacturing the light-emitting device.
     (1) According to one embodiment of the invention, a light-emitting device comprises:   

     a first light-emitting element; 
     a second light-emitting element; 
     a third light-emitting element placed between the first and second light-emitting elements; and 
     a bonding wire passing directly over the third light-emitting element and connecting the first light-emitting element with the second light-emitting element. 
     In the above embodiment (1) of the invention, the following modifications and changes can be made. 
     (i) A horizontal distance from the bonding wire to the center of a wire-bonding electrode on an upper surface of the third light-emitting element is not less than 1.75 times a diameter of the bonding wire. 
     (ii) The light-emitting device further comprises a sealing material for sealing the first, second and third light-emitting elements and the bonding wire. 
     (iii) At least one of a filler and a phosphor particle is dispersed into the sealing material. 
     (iv) The bonding wire comprises Ag. 
     (v) The first to the third light-emitting elements are aligned.
     (2) According to another embodiment of the invention, a method of manufacturing a light-emitting device comprises connecting a first light-emitting element with a second light-emitting element through a bonding wire such that the bonding wire passes directly over a third light-emitting element placed between the first and second light-emitting elements.   

     In the above embodiment (2) of the invention, the following modifications and changes can be made. 
     (vi) The bonding wire is installed such that a horizontal direction from the bonding wire to the center of a wire-bonding electrode on an upper surface of the third light-emitting element is not less than 1.75 times a diameter of the bonding wire. 
     (vii) The method further comprises sealing the first, second and third light-emitting elements and the bonding wire with a sealing material. 
     (viii) At least one of a filler and phosphor particle is dispersed into the sealing material. 
     (ix) The bonding wire comprises Ag. 
     Effects of the Invention 
     According to one embodiment of the invention, a light-emitting device can be provided that is constructed so as to allow the easy installation of the bonding wire and to prevent the breakage of the bonding wire even when the space between the plural light-emitting elements is narrowed, as well as a method of manufacturing the light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein: 
         FIG. 1  is a top view showing a light-emitting device in an embodiment of the invention; 
         FIG. 2  is an enlarged top view showing a portion of an element-mounting region of the light-emitting device; and 
         FIG. 3  illustrates a wire arrangement in which a bonding wire connecting between light-emitting elements passes directly over another light-emitting element. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment 
     Structure of Light-Emitting Device 
       FIG. 1  is a top view showing a light-emitting device  1  in the embodiment.  FIG. 2  is an enlarged top view showing a portion of an element-mounting region of the light-emitting device  1 . 
     The light-emitting device  1  has a substrate  10 , plural light-emitting elements  20  placed on the substrate  10 , a dam  14  surrounding the light-emitting elements  20 , and a sealing resin  15  filled in the dam  14  to seal the light-emitting elements  20 . The light-emitting device  1  may not have the sealing resin  15 . In  FIGS. 1 and 2 , illustration of the sealing resin  15  is omitted. 
     The substrate  10  is a substrate having wirings and is, e.g., a wiring substrate having a wiring pattern on a surface or a lead frame inserted board. 
     The light-emitting element  20  is a face-up type LED (Light Emitting Diode) or laser diode and has a chip substrate  22  and a crystal layer  23  formed thereon, as described later. A wire-bonding electrode  21  to which a bonding wire  16  is connected is formed on a surface of the crystal layer  23 . 
     The chip substrate  22  is, e.g., a sapphire substrate. The crystal layer  23  is, e.g., a GaN-based semiconductor layer formed on the chip substrate  22  by epitaxial crystal growth and has a light-emitting layer sandwiched between an n-type semiconductor layer and a p-type semiconductor layer. 
     The light-emitting elements  20  are coupled by the bonding wires  16 . The light-emitting elements  20  located at ends of the coupled elements are connected to wire-bonding terminals  12  by the bonding wires  16 . 
     In the configuration shown in  FIG. 1 , each wire-bonding terminal  12  is connected to an external connection terminal  11  via a wiring electrode  13  and receives power supply from the outside through the external connection terminal  11 . 
     As shown in  FIG. 2 , the light-emitting device  1  has a light-emitting element  20   a , a light-emitting element  20   b , a light-emitting element  20   c  placed between the light-emitting elements  20   a  and  20   b , and a bonding wire  16  which passes directly over the light-emitting element  20   c  to connect the light-emitting element  20   a  to the light-emitting element  20   b . The light-emitting elements  20   a ,  20   b  and  20   c  are included in the light-emitting elements  20 . 
     In case of connection between the light-emitting element  20   a  and the light-emitting element  20   b  which are arranged with the light-emitting element  20   c  interposed therebetween, the bonding wire  16  can be longer than for the connection between adjacent light-emitting elements, e.g., between the light-emitting elements  20   a  and  20   c . By this configuration, it is possible to easily form the bonding wire  16 , and wire breakage due to stress generated by expansion of the sealing resin  15 , which occurs when the bonding wire  16  is too short, can be also prevented. 
     A horizontal distance D from the bonding wire  16  connecting between the light-emitting elements  20   a  and  20   b  to the center of the wire-bonding electrode  21  on the upper surface of the light-emitting element  20   c  is preferably equal to or more than 1.75 times the diameter of the bonding wire  16 . 
     This is because it is possible to prevent contact of a ball bonding capillary with the bonding wire  16  connecting between the light-emitting elements  20   a  and  20   b  when subsequently connecting another bonding wire  16  to the wire-bonding electrode  21  of the light-emitting element  20   c . As a result, breakage of the bonding wire  16  due to contact with the capillary can be prevented. 
     In general, an outer diameter of a tip of a capillary is about 1.5 to 3.5 times a diameter of a bonding wire to be connected. Thus, it is possible to prevent contact of the capillary with the bonding wire  16  connecting between the light-emitting elements  20   a  and  20   b  by setting the minimum value of the horizontal distance D to 1.75 times the outer diameter of the bonding wire  16  which is half of 3.5 times, i.e., half of the maximum outer diameter of the tip of the capillary. 
     As a material of the bonding wire  16 , it is possible to use, e.g., Ag or Au. It is particularly preferable to use Ag which is excellent in electrical conductivity and light reflectance. In general, bonding wires formed of Ag are more likely to be broken than those formed of Au. In the present embodiment, however, the breakage of the bonding wire  16  can be prevented as described above and this allows Ag to be used as a material of the bonding wire  16 . 
     The dam  14  is formed of, e.g., a resin such as silicone-based resin or epoxy-based resin containing white pigment such as titanium oxide. 
     The sealing resin  15  is formed of, e.g., a transparent resin such as a silicone-based resin or an epoxy-based resin. The sealing resin  15  may additionally contain a filler formed of SiO 2 , etc., for scattering light or phosphor particle. When, for example, the emission color of the light-emitting element  20  is blue and the fluorescent color of the phosphor particles contained in the sealing resin  15  is yellow, the emission color of the light-emitting device  1  is white. 
     In the light-emitting device  1 , the layout, shape, size and number of the light-emitting elements  20  and a connection pattern thereof by the bonding wires  16 , etc., are not limited to those shown in  FIGS. 1 and 2  as long as the light-emitting device  1  has a structure in which the bonding wire  16  connecting two light-emitting elements  20  passes directly over another light-emitting element  20  sandwiched between such two light-emitting elements  20 . 
       FIG. 3  illustrates a wire arrangement in which the bonding wire  16  connecting between the light-emitting elements  20  passes directly over another light-emitting element  20 . Among the bonding wires  16  used in the light-emitting device  1 , only the bonding wire  16  connecting between the light-emitting elements  20   a  and  20   b  is shown in  FIG. 3 . 
     When the sealing resin  15  is formed as shown in  FIG. 3 , the larger the volume of the sealing resin  15  above and under the bonding wire  16 , the larger the expansion of the sealing resin  15  and the more likely it is that the bonding wire  16  is broken. 
     In a light-emitting device having a conventional structure, a sealing resin is naturally present under a bonding wire connecting light-emitting elements and has a thickness from an upper surface of a substrate to the bonding wire. 
     On the other hand, in the present embodiment, the sealing resin  15  present under the bonding wire  16  passing directly over the light-emitting element  20   a  only has a thickness from the upper surface of the light-emitting element  20   a  to the bonding wire  16  as shown in  FIG. 3 , and the volume of the sealing resin under the bonding wire is smaller than the conventional structure. 
     Therefore, in the present embodiment, the degree of expansion can be reduced when the sealing resin  15  expands and this allows breakage of the bonding wire  16  to be prevented. 
     Furthermore, it is preferable that at least one of a filler  17  and phosphor particle  18  be dispersed into the sealing resin  15 . The filler  17  and the phosphor particle  18  formed of an inorganic material have smaller thermal expansion coefficient than a resin constituting the sealing resin  15 . Therefore, it is possible to decrease average thermal expansion of the entire sealing resin  15  by dispersing the filler  17  and the phosphor particle  18 . 
     Effects of the Embodiment 
     In the embodiment, each bonding wire connecting between light-emitting elements is formed to pass directly over another light-emitting element, thereby allowing bonding wire breakage to be prevented. 
     Although the embodiment of the invention has been described above, the invention is not intended to be limited to the embodiment and the various kinds of modifications can be implemented without departing from the gist of the invention. 
     In addition, the invention according to claims is not to be limited to the embodiment. Further, all combinations of the features described in the embodiment are not necessary to solve the problem of the invention.