Patent Publication Number: US-11024771-B2

Title: Method for manufacturing light emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 16/268,158 filed on Feb. 5, 2019, which is a continuation application of U.S. patent application Ser. No. 15/841,769 filed on Dec. 14, 2017, now U.S. Pat. No. 10,243,106. The present application claims priority to Japanese Patent Application No. 2016-254851, filed on Dec. 28, 2016. The entire disclosures of U.S. patent application Ser. Nos. 16/268,158 and 15/841,769, and Japanese Patent Application No. 2016-254851 are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to a method for manufacturing a light emitting device. 
     Improvements in the crystal quality of light emitting diodes made it possible to increase the output and the luminance. As a consequence, they are utilized in various areas, such as general illumination and automotive lighting applications, and further quality improvements have been proposed. 
     For example, there is known a light emitting element having a structure in which the n-type electrode connected to the n-type semiconductor layer, which is exposed from the p-type semiconductor layer and the emission layer, is disposed on the p-type semiconductor layer via an insulation film in order to achieve high luminance and good luminance distribution. See, for example, Japanese Unexamined Patent Application Publication Nos. 2015-192099 and 2014-207267. 
     SUMMARY 
     One object of an embodiment of the present invention is to provide a light emitting device capable of achieving good luminance distribution and a method for manufacturing the same. 
     A method for manufacturing a light emitting device includes: providing a substrate defining a mounting region having a wiring pattern on an upper face thereof; forming a plurality of bumps for bonding a light emitting element to the wiring pattern in the mounting region of the substrate so that the bumps are arranged in a plurality of columns extending parallel to each other with a distance between adjacent ones of the bumps in one of the columns arranged closest to an outer edge of the mounting region is larger than a distance between adjacent ones of the bumps arranged on an inner side of the mounting region in a plan view, and so that the bumps include a plurality of first bumps and a plurality of second bumps with the first bumps including a plurality of first large bumps and a plurality of first small bumps each having a smaller surface area than each of the first large bumps in a plan view, with all the bumps in the one of the columns arranged closest to the outer edge of the mounting region are the same size; mounting the light emitting element onto the bumps in the mounting region of the substrate in a flip-chip manner so that the first bumps are bonded to a first electrode of the light emitting element and the second bumps are bonded to a second electrode of the light emitting element; and forming a cover member that covers lateral faces of the light emitting element and the bumps. 
     According to the present invention, a light emitting element capable of achieving good luminance distribution can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic perspective view of one embodiment of the light emitting device according to the present invention. 
         FIG. 1B  is a cross sectional view taken along line A-A′ in  FIG. 1A . 
         FIG. 2A  is a schematic plan view of the light emitting element used in the light emitting device in  FIG. 1A . 
         FIG. 2B  is a partial cross sectional view taken along line B-B′ in  FIG. 2A . 
         FIG. 3  is a schematic plan view of another light emitting element used in the light emitting device according to the present invention. 
         FIG. 4A  is a schematic enlarged plan view for explaining a substrate preparation step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4B  is a schematic enlarged plan view for explaining a bump forming step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4C  is a schematic enlarged plan view for explaining an element mounting step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4D  is a schematic enlarged plan view for explaining a step of disposing a light transmissive member in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4E  is a schematic enlarged plan view for explaining a cover member forming step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4F  is a schematic enlarged plan view for explaining a cover member forming step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 4G  is a schematic enlarged plan view for explaining a cover member forming step in the method for manufacturing a light emitting device according to the present invention. 
         FIG. 5  is a schematic plan view of a comparative light emitting element. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     One embodiment for practicing the present invention will be explained below with reference to the accompanying drawings. The embodiment described below, however, is an illustration for the purpose of embodying the technical concept of the present invention, and does not limit the present invention. The sizes of the members and their positional relationship shown in each drawing might be exaggerated for clarity of the explanations. Furthermore, the same designations and reference numerals represent members that are identical or similar in nature as a rule, and redundant explanations are omitted when appropriate. 
     Light Emitting Device 
     The light emitting device  10  related to the present embodiment, as shown in  FIGS. 1A and 1B , includes a substrate  11 , a light emitting element  20 , and a cover member  13 . 
     The substrate  11 , as shown in  FIGS. 1B, 4A, and 4B , defines a plurality of mounting regions (the boundary of the mounting regions is shown in dotted lines in  FIG. 4A ) each having a wiring pattern  14  on its upper face. On the wiring pattern  14 , first bumps  15  and second bumps  16  are arranged, and the light emitting element  20  is flip-chip mounted via the first bumps  15  and the second bumps  16 . Moreover, on the substrate  11 , the cover member  13  that covers the light emitting element  20 , the first bumps  15 , and the second bumps  16  is disposed. 
     The light emitting element  20 , as shown in  FIG. 2B , includes a semiconductor stack  23  which successively has a first semiconductor layer  21 , an emission layer, and a second semiconductor layer  22  as well as having a plurality of exposed portions  21   a  exposing the first semiconductor layer  21  from the second semiconductor layer  22  on the upper face side of the second semiconductor layer  22 ; an insulation film  24  which covers the semiconductor stack  23  and has openings  24   a  above the plurality of exposed portions  21   a ; a first electrode  25  connected to the exposed portions  21   a  at the bottom face of the openings  24   a  and partially disposed on the second semiconductor layer  22  via the insulation film  24 ; and a second electrode  26  connected onto the second semiconductor layer  22 . 
     The bumps include the first bumps  15  bonded to the first electrode  25 , and the second bumps  16  bonded to the second electrode  26 . In a plan view, the first bumps  15  are spaced apart from the exposed portions  21   a , and include two types having different surface areas. 
     The light emitting element  20  includes a plurality of exposed portions where the first semiconductor layer is exposed from the second semiconductor layer on the upper face side of the second semiconductor layer in the semiconductor stack  23 . If the exposed portions and the first bumps are arranged to overlap one another, i.e., if the first bumps are disposed directly above the exposed portions  21   a , the impact of flip chip mounting might cause a crack to form in the insulation film. It is preferable to position the first bumps apart from the exposed portions in a plan view so that the cracks are not allowed to form in the insulation film. In the light emitting device  10 , the first bumps  15  include large and small bumps, having different surface areas. Thus, a large number of first bumps can be densely arranged on the first electrode while avoiding the positions immediately above the exposed portions. This reduces the chances of localizing the current density to be supplied to the light emitting element, thereby reducing illuminance variance. 
     Furthermore, the high-density arrangement of the bumps directly under the light emitting element can increase the paths for dissipating the heat generated by the light emitting element during emission through the substrate via the bumps. The high-density arrangement facilitates the flow of the uncured resin material used for forming the cover member between the light emitting element and the substrate when the cover member covering the lateral faces of the light emitting elements and the bumps is formed on the substrate, reducing the chances of void formation or the like directly under the light emitting element. This can prevent light from leaking from the lower face of the light emitting element, as well as effectively preventing the light emitting element from separating from the substrate which would otherwise be caused by the expansion of a void as the temperature surrounding the light emitting device changes. Thus, a higher quality light emitting device can be provided. 
     Substrate  11   
     The substrate  11  has a wiring pattern  14  on the upper face thereof, and the light emitting element  20  is flip-chip mounted on the wiring pattern  14  via bumps  15  and  16 . Examples of the substrate materials include insulating materials, such as a glass fiber reinforced epoxy, resins, and ceramics, as well as a metal material with an insulating material formed on the surface thereof. Among all, a ceramic material which is highly heat resistant and weather resistant is preferable for the substrate. Ceramics materials include alumina, aluminum nitride, and the like. 
     The substrate  11  has multiple wiring patterns  14  on the upper surface thereof. 
     Such a wiring pattern  14  may be anything that can supply electric current to the light emitting element, and can be formed using any material, thickness, or shape ordinarily employed in the art. Specifically, the wiring pattern  14  can be formed, for example, using a metal, such as copper, aluminum, gold, silver, platinum, titanium, tungsten, palladium, iron, nickel, or the like, or an alloy containing these. Particularly, the outermost surface of the wiring pattern formed on the upper face of the substrate is preferably covered with a highly reflective material, such as silver or gold, in order to efficiently extract light from the light emitting element  20 . The wiring pattern can be formed by electroplating, electroless plating, vapor deposition, sputtering, or the like. In the case of using Au bumps for mounting the light emitting element on the substrate, for example, using Au as the outermost surface of the wiring pattern can improve the bonding between the substrate and the substrate. 
     The wiring pattern  14  preferably has a pair of positive and negative patterns on the upper face of the substrate  11 . Such wiring pattern allows for the connection of the first electrode of the first semiconductor layer and the second electrode of the second semiconductor layer in the light emitting element by way of flip chip mounting. The wiring pattern  14  may be disposed not only on the upper surface of the substrate  11 , but also inside and/or on the lower surface thereof 
     Bumps  15  and  16   
     The wiring pattern  14  has, on the upper surface, first bumps  15  to be connected to the first electrode, and second bumps  16  to be connected to the second electrode, of the light emitting element used for flip chip mounting of the light emitting element described later. Multiple bumps are disposed for each. In the present embodiment, the first bumps  15 , as shown in  FIG. 4B , include two types having different surface areas. Examples of the plan view shapes of the bumps include a circular shape, substantially circular shape, or the like. The two types of first bumps having different surface areas include first large bumps  15 B, and first small bumps  15 S each having a smaller surface area than a first large bump  15 B. The second bumps  16  may have a different size from the first bumps  15 , but preferably have a similar size to that of the first large bumps  15 B. The surface areas of the two types of first bumps  15  are appropriately set in accordance with the size or the like of the light emitting element used. From the standpoint of heat dissipation and bonding strength, the larger the total bump surface area bonded to a single light emitting element, the more preferable it is. Considering the layout of the exposed portions, however, the length of the longest line segment (e.g., the diameter in the case of a circular shape) of each first large bump  15 B is preferably smaller than the distance between the centers of two adjacent exposed portions. It is preferable for the first small bumps  15 S to each have about 30 to 70% of the surface area of each first large bump. This allows the first small bumps to be disposed in the regions where the first large bumps cannot be disposed, thereby increasing the total bump surface area. 
     By providing the first bumps having two different surface areas in this manner, the bumps can be densely arranged on the surface of the light emitting element without overlapping the exposed portions arranged on the semiconductor stack. This can distribute the current density supplied to the light emitting element, thereby attenuating luminance variance. 
     In the case where the light emitting element  20  has a rectangular plan view shape, in particular, it is preferable to arrange the first small bumps  15 S at least in the vicinity of two opposing sides of the rectangular shape, along the sides. They may be arranged in the vicinity of each side of the two pairs of opposing sides, along each side. Such a layout enables uniform injection of electric current even in the vicinity of the perimeter of the light emitting element, thereby achieving an even more uniform luminance distribution and ensuring uniform in-plane heat dissipation. 
     The two types of first bumps having different surface areas may have about the same height, or have different heights. For example, the first large bumps  15 B preferably have a larger height than the first small bumps. Since the first small bumps  15 S are arranged in narrow regions in the regions where the first large bumps  15 B cannot be disposed, giving them a lower height than the first large bumps  15 B can reduce the impact resulting from bonding as compared to that applied to the first large bumps  15 B, thereby more effectively preventing the bumps from being crushed and expanding their surface areas. 
     Although the first large bumps  15 B and the first small bumps  15 S may be regularly or randomly arranged, they are preferably regularly arranged so that the current density supplied to the light emitting element  20  would not be localized. 
     The first bumps  15  and the second bumps  16  can be formed with, for example, gold, silver, copper, tin, platinum, zinc, nickel, or their alloys, and can be formed by using, for example, stud bumps known in the art. Stud bumps can be formed using a stud bump bonder, wire bonding apparatus, or the like. 
     Light Emitting Element  20   
     The light emitting element  20 , as shown in  FIG. 2B , has a semiconductor stack  23  in which a first semiconductor layer  21 , an emission layer, and a second semiconductor layer  22  are stacked in that order, an insulation film  24 , a first electrode  25 , and a second electrode  26 . The semiconductor stack  23  has, on the upper face side of the second semiconductor layer  22 , a plurality of exposed portions  21   a  exposing the first semiconductor layer  21  from the second semiconductor layer  22  on the upper face side of the second semiconductor layer  22 . The insulation film  24  covers the semiconductor stack  23 , and has openings  24   a  above the plurality of exposed portions  21   a . The first electrode  25  is connected to the exposed portions  21   a  at the openings  24   a , and is partly disposed on the second semiconductor layer  22  via the insulation film  24 . The second electrode  26  is electrically connected to the second semiconductor layer  22 , and is disposed on the second semiconductor layer  22 . 
     Examples of the plan view shapes of the light emitting element and/or the semiconductor stack include polygons, such as a rectangle or hexagon, a polygon with rounded corners, circle, ellipse, or the like. 
     Semiconductor Stack  23   
     The semiconductor stack  23  is formed by successively stacking a first semiconductor layer  21  (e.g., n-type semiconductor layer), an emission layer, and a second semiconductor layer  22  (e.g., p-type semiconductor layer) on a growth substrate  27 . In the state of being incorporated in a light emitting element  20 , however, the semiconductor stack can be one from which the growth substrate  27  has been removed. 
     Examples of the first semiconductor layer, the emission layer, and the second semiconductor layer include various semiconductors, such as group III-V compound semiconductors, group II-VI compound semiconductors, and the like. Specific examples include nitride-based semiconductor materials such as In X Al Y Ga 1-X-Y N (0≤X, 0≤Y, X+Y≤1); InN, AlN, GaN, InGaN, AlGaN, InGaAlN, or the like can be used. Any film thickness or layer structure known in the art can be used for each layer. 
     Growth Substrate  27   
     For the growth substrate  27 , any that allows for epitaxial growth of the semiconductor layers can be used. Examples of such growth substrate materials include insulating substrates, such as sapphire (Al 2 O 3 ), spinel (MgAl 2 O 4 ), or the like. 
     Exposed Portions  21   a    
     The semiconductor stack  23  has multiple exposed portions  21   a  where the second semiconductor layer  22  and the emission layer are removed across their entire thicknesses, exposing the first semiconductor layer  21  from the second semiconductor layer and the emission layer. In other words, the semiconductor stack  23  has holes on the surface on the second semiconductor layer side, and the first semiconductor layer  21  is exposed at the bottom faces of the holes. The second semiconductor layer  22 , the emission layer, and the first semiconductor layer  21  are exposed at the lateral faces of the holes. 
     Although the shape, the size, the positions, and the number of the exposed portions can be appropriately set in accordance with the intended size, shape, electrode pattern, or the like of the light emitting element, multiple exposed portions are preferably formed on the inner side of the edges of the semiconductor stack. The exposed portions are preferably disposed in a regular sequence. This can attenuate illuminance variance of the light emitting element thereby allowing light to be uniformly extracted. 
     The exposed portions  21   a  are electrically connected to the first electrode described later. The first electrode connected to the exposed portions is formed on the second semiconductor layer via the insulation film  24  discussed later. Such exposed portions are preferably arranged so as to be spaced apart from one another in a plan view, more preferably arranged in a regular sequence while maintaining a certain distance from one another. The exposed portions may all have the same shape and size, may individually or some of them may have different shapes and sizes. However, the exposed portions preferably have about the same size and shape. Since the exposed portions are the regions having no emission layer, regularly arranging multiple exposed regions of about the same size can attenuate localization of the emission area or the amount of the electrical current supplied. As a result, luminance variance of the light emitting element can be attenuated as a whole. 
     Examples of the shapes of the exposed portions include a circle, ellipse, or polygon, such as a triangular, rectangular, or hexagonal shape, or the like. Among all, a circular shape, or substantially circular shape (e.g., ellipse or polygon with at least six sides) is preferable. The size of the exposed portions can be appropriately adjusted based on the size of the semiconductor stack and the output, luminance, or the like of the light emitting element desired. The size of about several ten to several hundred μm in diameter, for example, is preferable. From another perspective, the diameter is preferably about 1/20 to ⅕ of a side of the semiconductor stack. 
     The total area of the exposed portions arranged on the inner side of the edges of the semiconductor stack is preferably 30% at most, 25% at most, 18% at most, or 15% at most of the surface area of the semiconductor stack. Setting the total area in these ranges can attain balance in the electric current supplied to the light emitting element, thereby attenuating illuminance variance attributable to localization of the power supplied. 
     Insulation Film  24   
     The insulation film  24  covers the upper face and the lateral faces of the semiconductor stack  23 , and has openings  24   a  above the exposed portions  21   a . Because the insulation film  24  covers the semiconductor stack  23  and have the openings  24   a  above the exposed portions  21   a , the first electrode  25  can be formed over a more extensive area of the upper face of the insulation film  24 . 
     The insulation film  24  is formed using a material and thickness capable of securing electrical insulation known in the art. Specifically, a metal oxide or metal nitride can be used for the insulation film  24 ; for example, at least an oxide or nitride selected from the group consisting of Si, Ti, Zr, Nb, Ta, and Al can suitably be used. 
     First Electrode  25  and Second Electrode  26   
     The first electrode  25  and the second electrode  26  are disposed on the upper face side of the semiconductor stack (i.e., on the second semiconductor layer side opposite the growth substrate). The first electrode and the second electrode may be electrically connected to the first semiconductor layer and the second semiconductor layer, respectively, via the reflective electrode described later, instead of being directly connected thereto. 
     The first electrode and the second electrode can be formed using metals such as Au, Pt, Pd, Rh, Ni, W, Mo, Cr, Ti, Al, Cu, or their alloys as a single layer film or multilayered film. Specifically, these electrodes can be formed with a multilayered film, such as Ti/Rh/Au, Ti/Pt/Au, W/Pt/Au, Rh/Pt/Au, Ni/Pt/Au, Al—Cu alloy/Ti/Pt/Au, Al—Si—Cu ally/Ti/Pt/Au, Ti/Rh, or the like, stacked from the semiconductor layer side. Any film thickness used in the art can be employed. 
     The shapes of the first electrode and the second electrode, in the case of a rectangular semiconductor stack, are preferably similarly rectangular or substantially rectangular. The first electrode and the second electrode are preferably arranged in parallel and alternately in one direction in a single semiconductor stack in a plan view. For example, it is preferable to arrange them so that the first electrode interposes the second electrode in a plan view. 
     The first electrode is electrically connected to the exposed portions arranged on the second semiconductor layer side of the semiconductor stack described above. In this case, the first electrode is preferably connected so as to cover the exposed portions, more preferably connected to all exposed portions integrally. Accordingly, the first electrode is disposed not only on the first semiconductor, but also above the second semiconductor layer. In this case, the first electrode  25  is disposed on the lateral faces (i.e., the lateral faces of the emission layer and the second semiconductor layer) of the holes that form the exposed portions and the second semiconductor layer via the insulation film  24 . 
     The second electrode is disposed on the second semiconductor layer of the semiconductor stack described above, and is electrically connected to the second semiconductor layer. The second electrode may be in direct contact with the second semiconductor layer, but is preferably disposed on the second semiconductor layer via the reflective electrode discussed later. 
     Reflective Electrode 
     As shown in  FIG. 2B , the light emitting element  20  has a reflective electrode  28  interposed between the second electrode and the second semiconductor layer. 
     For the reflective electrode  28 , silver, aluminum, or an alloy having either of these as a major component can be used, and silver or a silver alloy having high reflectance for the light emitted from the emission layer, in particular, is more preferable. The reflective electrode  28  preferably has a thickness that can effectively reflect the light emitted from the emission layer, for example, about 20 nm to 1 μm. The larger the contact area between the reflective electrode and the second semiconductor layer, the more preferable it is. Accordingly, it is preferable to dispose the reflective electrode  28  also between the first electrode  25  and the second semiconductor layer  22 . Specific examples of the total surface area of the reflective electrode  28  include at least 50%, at least 60%, or at least 70% of the surface area of the semiconductor stack. 
     In the case where the reflective electrode  28  contains silver, a protective layer  29  that covers the upper face thereof, more preferably the upper face and the lateral faces thereof, may be provided in order to prevent the migration of silver. 
     The protective layer  29  may be formed using a conductive material, such as a metal, alloy, or the like, usually used as an electrode material, or may be formed using an insulating material. Examples of conductive materials include a single layer or multilayered film containing a metal, such as aluminum, copper, nickel, or the like. Examples of insulating materials include those mentioned earlier with reference to the insulation film  24 , and SiN, among all, is preferably used. An SiN is a dense film and thus excels in preventing moisture penetration. The thickness of the protective layer  29  is, for example, about several hundred nm to several μm for effectively preventing silver migration. 
     In the case of forming the protective layer  29  with an insulating material, providing an opening in the protective layer  29  above the reflective electrode can achieve electrical connection between the reflective electrode and the second electrode. 
     In the case where the light emitting element  20  has the reflective electrode  28  and the protective layer  29  on the second semiconductor layer, the insulating film  24  that covers the semiconductor stack  23  covers the reflective electrode  28  and the protective layer  29 , and has an opening directly under the second electrode  26  whereby the second electrode  26  and the reflective electrode  28  are electrically connected. 
     Cover Member  13   
     The cover member  13 , as shown in  FIG. 1B , covers the light emitting element  20 , the first bumps  15 , the second bumps  16 , and part of or the entire upper face of the substrate  11 . Above all, the cover member  13  preferably entirely covers the lateral faces of the light emitting element  20 , between the light emitting element  29  and the substrate  11 , the upper face of the substrate  11 , and the lateral faces of the first bumps  15  and the second bumps  16 . 
     The cover member  13  can be formed with a resin having light reflecting, transmitting, or light shielding properties, or any such resin containing a light reflecting substance, phosphor, diffusing agent, coloring agent, or the like. Among all, the cover member preferably has light reflecting and/or light shielding properties. Any resin, light reflecting substance, and the like ordinarily used in the art can be used to structure the cover member. 
     Examples of resins include a resin containing one or more, or a hybrid resin, of silicone resins, modified silicone resins, epoxy resins, modified epoxy resins, and acrylic resins. Examples of light reflecting substances include titanium oxide, silicon oxide, zirconium oxide, potassium titanate, alumina, aluminum nitride, boron nitride, mullite, and the like. 
     The material that structures the cover member  13  preferably includes a resin having high fluidity and is curable by heat or irradiation of light from the standpoint of ease of penetration between the light emitting element and the substrate, as well as void prevention. Such a material, for example, has fluidity indicated by the viscosity of 0.5 to 30 Pa·s. Moreover, the amount of reflection and the amount of transmittance can be varied by the content of the light reflecting substance or the like in the material that structures the cover member  13 . For example, the cover member preferably contains at least 20 wt % of a light reflecting substance. 
     The cover member  13  can be formed by, for example, injection molding, potting, resin printing, transfer molding, compression molding, or the like. 
     Light Transmissive Member  17   
     As shown in  FIG. 1A  and  FIG. 1B , the light emitting device  10  has a light transmissive member  17  on the light emitting element  20 . The light emitting element  20  is flip-chip mounted on the wiring pattern using the face having the first and second electrodes as the lower face. The light emitting element  20  uses the opposing upper face as the principal light extraction face which is bonded to the lower face of the light transmissive member  17 . 
     The light transmissive member  17  covers the light extraction face of the light emitting element and is capable of transmitting at least 50% or at least 60%, preferably at least 70% of the light emitted by the light emitting element to be externally released. The light transmissive member can contain a light diffusing agent and/or a phosphor capable of converting the wavelength of at least part of the light emitted from the light emitting element  20 . 
     The lower face of the light transmissive member preferably has an area which is about 80 to 150% of the upper face area of the light emitting element. The lower face perimeter of the light transmissive member preferably coincides with, or is positioned on the inside or the outside of, the upper face perimeter of the light emitting element. In other words, in a plan view, one of the light emitting element&#39;s upper face and the light transmissive member&#39;s lower face is preferably included in the other. The thickness of the light transmissive member, for example, is 50 to 300 μm. 
     The light transmissive member can be formed with, for example, a resin, glass, inorganic material, or the like. Examples of light transmissive members containing a phosphor include a phosphor sintered body as well as a resin, glass, or other inorganic material containing a phosphor. The light transmissive member may be a sheet-shaped molded resin, glass, inorganic material or the like, having a resin layer containing a phosphor formed on the surface thereof. The higher the transparency of the light transmissive member, the more reflection it achieves at the interface with the cover member, thereby increasing the luminance. 
     Examples of the phosphors to be contained in the light transmissive member include, in the case where a blue or ultraviolet light emitting element is used as the light emitting element  20 , cerium-activated yttrium aluminum garnet-based phosphors (YAG:Ce); cerium-activated lutetium aluminum garnet-based phosphors (LAG:Ce); europium- and/or chromium-activated nitrogen-containing calcium aluminosilicate-based phosphors (CaO—Al 2 O 3 —SiO 2 :Eu); europium-activated silicate-based phosphors ((Sr,Ba) 2 SiO 4 :Eu); nitride-based phosphors, such as β-SiAlON phosphors (e.g., Si 6-Z Al Z O Z N 8-Z :Eu (0&lt;Z&lt;4.2)), CASN-based phosphors, SCASN-based phosphors or the like; KSF-based phosphors (K 2 SiF 6 :Mn); sulfide-base phosphors, and quantum dot phosphors. By combining these phosphors with a blue or ultraviolet light emitting element, light emitting devices of various emission colors (e.g., a white light emitting device) can be produced. In the case of including such a phosphor in the light transmissive member, the concentration of the phosphor is preferably, for example, about 5 to 50%. 
     The light transmissive member is bonded to cover the light extraction face of the light emitting element. The light transmissive member and the light emitting element can be bonded via a bonding material  18 . For the bonding material  18 , any known resin, such as epoxy or silicone, can be used. In bonding the light transmissive member to the light emitting element, moreover, a direct bonding method, such as crimping, sintering, surface activated bonding, atomic diffusion bonding, or hydroxide catalysis bonding, may alternatively be used. 
     In the case where the light emitting device  10  includes a light transmissive member  17 , it is preferable to cover the lateral faces of the light transmissive member  17  in part or in whole with the cover member  13 . 
     The light emitting device may optionally include other devices and electronic parts, such as a protective device  19  or the like. These devices and parts are preferably embedded in the cover member  13 . 
     Method for Manufacturing a Light Emitting Device 
     The light emitting device according to the present embodiment primarily has a substrate preparation step, a bump forming step, a light emitting element mounting step, and a cover member forming step. The materials and layout of the members are as explained above with reference to the light emitting device  10 , and thus the explanations here will be omitted when appropriate. 
     Furthermore, a step of disposing a light transmissive member  17  on the light emitting element  20  and a step of mounting electronic parts, such as a protective device, can optionally be included prior to forming the cover member  13 . 
     Substrate Preparation Step 
     A substrate  11  having a wiring pattern  14  formed on the upper face thereof is prepared. As shown in  FIGS. 4A and 4B , the substrate  11  simply needs to have on the surface thereof a wiring pattern  14 , which include a first wiring pattern  14   a  to be connected to the first electrode of the light emitting element  20  and a second wiring pattern  14   b  to be connected to the second electrode of the light emitting element  20 , formed as the wiring pattern  14 . 
     In order to simultaneously manufacture multiple light emitting devices, a collective body of the substrates  11  is preferably used. Using the collective body of the substrates allows multiple light emitting devices to be collectively formed, thereby increasing the production efficiency. The collective body of the substrates can ultimately be divided into individual light emitting devices as shown in  FIG. 4G . 
     Bump Forming Step 
     As shown in  FIG. 4B , two types of first bumps  15  having different surface areas, i.e., first small bumps  15 S each having a small surface area and first large bumps  15 B each having a larger surface area than the first small bumps, are formed on the first wiring pattern  14   a . Moreover, on the second wiring pattern  14   b , second bumps  16  are formed. The second bumps  16  can each have a give surface area, but are preferably sized about the same as the first large bumps  15 B or the first small bumps  15 S for the purpose of increasing the production efficiency. It is preferable to suitably select the size of the second bumps by taking into consideration the plan view shape of the second electrode to be bonded so that the total surface area of the second bumps is large. 
     The layouts of the bumps relative to the wiring pattern are determined in accordance with the exposed portions, the electrode layout, or the like of the light emitting element to be mounted thereon while enabling the mounting of the light emitting element discussed later. 
     The first bumps and the second bumps can be formed by using, for example, a commercially available stud bump bonder or wire bonder. Specifically, the tip of the metal wire fed through the capillary of a stud bump bonder is melted to form a ball and the formed ball is bonded to a wiring pattern  14 , followed by separating the bonded ball from the metal wire. Stud bumps are formed on the wiring pattern in this manner. It is preferable to separate a ball from the metal wire so that the upper end thereof is relatively flat by lifting the capillary while holding the metal wire after bonding the ball onto a wiring pattern and parallel transferring the capillary thereby to allow the edge provided at the capillary tip to scrape and cut the deformed ball. 
     The surface area of a bump can be sized by suitably adjusting the amount of metal wire to be melted, the tip shape of the capillary, and the pressing force. A bump can have any height by suitably adjusting the height to which capillary is lifted, the parallel transfer timing, or the like. The upper end of a bump may alternatively be flattened by processes, such as etching, blasting, polishing, or the like. The tip end of a stud bump may be softened or smoothed by allowing the tip end to melt and recrystallize using sparks generated by applying a voltage to the formed stud bump. 
     The bumps having two different surface areas are formed by way of the methods described above. This can reduce the distance between the bumps thereby highly densely arranging the bumps. Furthermore, softening the upper ends of the stud bumps allows the upper ends to be readily deformed during flip chip mounting and facilitates bonding to the electrodes of the light emitting element. This can achieve high-strength bonding even at room temperature. 
     The intervals between the first bumps, and between the second bumps, can be suitably set based on the size of the light emitting element, the number of bumps, or the like. For example, considering the fluidity of the resin material used in the cover member forming step described later, the distance between the second bumps  16  arranged in one direction is preferably set smaller than the distance between the first large bumps  15 B arranged in the same direction. Similarly, the distance between the first small bumps arranged in the same direction is preferably set smaller than the distance between the first large bumps. Specifically, the distance between the first large bumps  15 B is, for example, 20 to 50 μm, the distance between the second bumps  16  is, for example, 0 to 20 μm, and the distance between the first small bumps  15 S is, for example, 50 to 80 μm. 
     From the heat dissipation standpoint, moreover, the larger the bonding area between the bumps and the light emitting element, the more preferable it is. For example, the total surface area of the first bumps connected to the first electrode is preferably at least 25% of the surface area of the first electrode. The total surface area of the second bumps connected to the second electrode is preferably at least 50% of the surface area of the second electrode. 
     Element Mounting Step 
     As shown in  FIG. 4C , the light emitting element  20  is flip-chip mounted on the wiring pattern  14 . The first electrode  25  and the second electrode  26  of the light emitting element  20  are bonded to the first bumps  15  and the second bumps  16 , respectively. In this case, the first bumps  15  are arranged so that none of the first large bumps  15 B and the first small bumps  15 S overlap the exposed portions  21   a  of the first semiconductor layer of the light emitting element  20  in a plan view. Arranging the bumps spaced apart from the exposed portions in this manner can prevent cracks from forming in the light emitting element  20  attributable to the pressing force applied to the light emitting element when it is bonded onto the bumps. As shown in  FIG. 2A  and  FIG. 2B , the first electrode  25  of the light emitting element  20  is formed on the second semiconductor layer via the insulation film  24 . The insulation film  24  covers the semiconductor stack  23 , and has the openings  24   a  above the exposed portions  21   a . The first electrode  25  is formed to be electrically connected to the first semiconductor layer  21  at the bottom faces of the openings  24   a , and to cover the lateral faces of the exposed portions  21   a  (i.e., lateral faces of the holes that form the exposed portions  21   a ) and the upper face of the second semiconductor layer via the insulation film  24  that covers the semiconductor stack. In the semiconductor stack  23 , steps are formed by the surface of the second semiconductor layer and the exposed portions  21   a . If a large load is applied to any of the steps, a crack might be formed in the light emitting element  20 . The metal oxide or metal nitride used to form the insulation film  24 , in particular, is hard, brittle, and thus susceptible to cracks, as compared to the metal material used to form the electrodes. A crack occurring in the insulation film would allow the first electrode to be in electrical conduction with the second semiconductor layer, which would likely cause the light emitting element  20  to have a short circuit. In other words, by arranging the bumps spaced apart from the exposed portions in a plan view, the occurrence of cracks in the insulation film  24  can effectively be avoided. Being arranged spaced apart herein means that the outer edges of the bumps do not overlap the outer edges of the exposed portions in a plan view even after the light emitting element is pressed to be connected to the bumps where the pressure laterally expands the bumps to increase their surface areas. 
     In the case where the first small bumps  15 S among the first bumps are arranged in the vicinity of the two opposing sides of the light emitting element  20 , the expansion of the bumps&#39; surface areas caused by the pressure applied when the bumps are bonded to the light emitting element is smaller as compared to the first large bumps  15 B. Thus, short circuits attributable to the laterally expanded bumps creeping onto the lateral faces of the light emitting element  20 , or the like, can be avoided. Furthermore, even if the light emitting element  20  is warped, setting a smaller height for the first small bumps  15 S than that for the first large bumps allows the light emitting element to attain an appropriate pressure load, bump expansion, and connection with the bumps corresponding to the warp. 
     Step of Disposing Light Transmissive Member 
     The method for manufacturing a light emitting device according to the present embodiment may have a step of disposing a light transmissive member. In the step of disposing a light transmissive member, as shown in  FIG. 4D , a light transmissive member  17  is disposed to cover the upper face of the light emitting element. The light transmissive member  17  can be disposed by using any transparent bonding material  18  known in the art. 
     The step of disposing a light transmissive material may be performed before the element mounting step; for example, in the case of bonding the light transmissive member and the light emitting element without using a bonding material  18 , the step of disposing a light transmissive member is preferably performed before the element mounting step. 
     Cover Member Forming Step 
     The cover member forming step is a step of forming a cover member  13  on the substrate  11  that surrounds the light emitting element  20  which has been mounted. The cover member  13  is formed to cover the lateral faces of the bumps at the lower face of the light emitting element  20 , i.e., between the light emitting element  20  and the substrate  11 . In the case where the light emitting device is provided with a light transmissive member  17 , the cover member  13  is formed to cover the lateral faces of the light transmissive member  17 . At this point, exposing the upper face of the light transmissive member  17  from the cover member  13  produces a light emitting device  10  having the upper face of the light transmissive member  17  as the emission face. 
     The cover member  13  can be formed by placing a nozzle of a resin dispenser above the substrate  11  and moving the nozzle while dispensing an uncured resin from the nozzle tip. 
     The cover member  13  is preferably formed in multiple resin applications. 
     First, as shown in  FIG. 4E , the uncured resin material is dispensed between the multiple light emitting devices along the borders of the devices that are arranged in rows and columns on the collective body of the substrates every other row or column, for example, at the position indicated by the arrow in  FIG. 4E . The resin material flows on the substrate  11  and under the light emitting element  20  while wetting and spreading over the substrate  11  as shown in  FIG. 4F . 
     Next, the resin material is dispensed similarly between the rows or columns of the devices, one row or column at a time, for example, as indicated by the arrows in  FIG. 4F , to cover the lateral faces of the light emitting elements. 
     Supplying the resin material in two applications in this manner can reduce the occurrence of voids in the resin material disposed under the light emitting elements. In other words, supplying the resin material every other row or column during the first application allows the resin to flow from one side, thereby allowing the air to escape to the other side. After disposing the resin material under the light emitting elements, the resin material is supplied for the second time to form the resin that covers the lateral faces of the light emitting elements. In this manner, the resin material having fluidity can effectively penetrate into the space between the light emitting elements and the substrates. 
     Furthermore, the highly densely arranged bumps discussed earlier facilitate the flow of the resin material along the narrow spaces between the bumps (the so-called capillary action), allowing the cover member to be formed in the appropriate locations in a simplified manner while preventing the occurrence of voids. 
     In the present embodiment, moreover, the bumps are arranged so that the distance between the bumps located in the center of each light emitting element is shorter than the distance between the bumps located near the edges of the light emitting element along the direction of the flow of the resin material under the light emitting element, i.e., the direction perpendicular to the direction of the movement of the nozzle that supplies the resin material on the upper face of the substrate  11 . This facilitates the flow of the resin material in the center of each light emitting element by utilizing the capillary action mentioned above, thereby reducing the occurrence of voids attributable to the resin material infiltrating from the edges. In the present embodiment, along the direction perpendicular to the direction of the nozzle movement, the first small bumps  15 S are arranged at the outermost locations, i.e., near the edges of the substrate  11 , while arranging the second bumps  16  each having about the same size as that of the first large bumps  15 B at the innermost locations, i.e., in the vicinity of the center directly under the light emitting element, more densely than the first large bumps  15 B. 
     Dividing Light Emitting Devices 
     As shown in  FIG. 4G , the light emitting device  10  having a single light emitting element  20  mounted thereon can be obtained by dividing the substrate  11  having the cover member  13  formed thereon along the dotted lines in  FIG. 4G  into individual light emitting devices  10 . The substrate can be divided by using any means known in the art, such as a dicing saw. 
     Example 1 
     The light emitting device according to Example 1 was produced by using the method for manufacturing a light emitting device described in the foregoing, using a light emitting element  20  having a plan view shape of substantially a square, 1.0 mm per side. 
     As shown in  FIG. 2A  and  FIG. 2B , the light emitting element  20  has a second electrode  26  which has a narrow strip shape and is disposed vertically across the central portion of the element, and a first electrode  25  disposed on both sides of the second electrode  26 . The first electrode  25  located on both sides of the second electrode  26  is continuous at both long side ends of the second electrode  26 . In other words, the first electrode  25  is disposed to surround the narrow strip shaped second electrode  26 . The width, i.e., the short side length, of the second electrode  26  is about 140 μm, and the width of the first electrode interposing the second electrode is about 370 μm on each side. Exposed portions  21   a  of the first semiconductor layer are arranged under the first electrode  25 . The exposed portions  21   a  are each substantially circular in shape having a diameter of 53 μm, and 7×3 pieces of the exposed portions are arranged at equal intervals on each side of the second electrode  26 . The distance between two opposing exposed portions that interpose the second electrode  26  is, for example, 0.28 μm. The distance from an edge of the semiconductor stack to the exposed portions that are closest to the edge is, for example, 0.07 μm. 
     In the substrate  11  having such a light emitting element  20  mounted thereon, the first bumps  15  are arranged at the positions spaced apart from and not overlapping the exposed portions  21   a  in the state where the light emitting element  20  is mounted on the wiring pattern  14 ; for example, at the positions indicated by the two-dot chain lines in the light emitting element  20  shown in  FIG. 2A . Among the first bumps, the first large bumps  15 B are each arranged per region of the smallest square having the exposed portions  21   a  at four corners. On the first electrode  25  in each of the regions on both sides of the second electrode, 6×2 pieces of the first large bumps  15 B are disposed. The first large bumps  15 B are substantially circular in shape and about 100 μm in diameter. The first small bumps  15 S are arranged between the exposed portions  21   a  arranged along the edges of the semiconductor stack, 6×1 pieces per side. The first small bumps  15 S are substantially circular in shape and about 80 μm in diameter. 
     The second bumps  16 , 8×1 pieces, are arranged at equal intervals along the second electrode  26  in the state where the light emitting element  20  is mounted on the wiring pattern  14 . The second bumps  16  are circular in shape and about 100 μm in diameter. The distance between two adjacent second bumps  16  is smaller than the distance between two adjacent first large bumps  15  arranged in the same direction. 
     In the light emitting device according to Example 1, the surface area of the first electrode  25  is about 0.694 mm 2 , and the total surface area of the first bumps is about 0.235 mm 2 . Thus, the total surface area of the first bumps is about 34% of the surface area of the first electrode. The surface area of the second electrode  26  is about 0.120 mm 2 , and the total surface area of the second bumps is about 0.063 mm 2 . Thus, the total surface area of the second bumps is about 53% of the surface area of the second electrode. 
     Example 2 
     The light emitting device according to Example 2 was produced by using the method for manufacturing a light emitting device described in the foregoing, using a light emitting element  30  having a plan view shape of substantially a square, 0.8 mm per side. 
     As shown in  FIG. 3 , the light emitting element  30 , similar to the light emitting element  20  of Example 1, has a second electrode  56  which has a narrow strip shape and is disposed to divide the element in the middle, and a first electrode  55  which is disposed to surround the second electrode  56 . 
     Exposed portions  31   a  of the first semiconductor layer are disposed under the first electrode  55 . The exposed portions  31   a  which are substantially circular in shape, 53 μm in diameter, are regularly arranged at equal intervals, for example, with a distance between the centers of two adjacent exposed portions of 0.16 mm, on both sides of the second electrode  56 , 5×2 pieces each. The distance between the centers of two opposing exposed portions that interpose the second electrode  56  is, for example, 0.28 mm. The distance from an edge of the semiconductor stack to the centers of the exposed portions that are closest to the edge is, for example, 0.007 mm. 
     In the substrate  11  having such a light emitting element  30  mounted thereon, the first bumps  35  and the second bumps  36  are arranged at the positions spaced apart from and not overlapping the exposed portions  21   a  in the state where the light emitting element  30  is mounted on the wiring pattern; for example, at the positions indicated by the two-dot chain lines in the light emitting element  30  shown in  FIG. 3 . Among the first bumps, the first large bumps  15 B are each arranged per region of the smallest square having the exposed portions  21   a  at four corners. On the first electrode  55  in each of the regions on both sides of the second electrode  56 , 4×1 pieces of the first large bumps  35 B are disposed. The first large bumps  35 B are substantially circular in shape and about 100 μm in diameter. The first small bumps  35 S are arranged between the exposed portions  21   a  arranged along the edges of the semiconductor stack, 4×1 pieces per side. Moreover, a piece of first small bump  35 S is arranged at each end of each column of the first large bumps  35 B. The first small bumps  35 S are substantially circular in shape and about 80 μm in diameter. 
     The second bumps  36 , 6×1 pieces, are arranged at equal intervals along the second electrode  56  in the state where the light emitting element  30  is mounted on the wiring pattern. The second bumps  36  are circular in shape and about 100 μm in diameter. The distance between two adjacent second bumps  36  is smaller than the distance between two adjacent first large bumps  35  which are arranged in the same direction. 
     In the light emitting device according to Example 2, the surface area of the first electrode  55  is about 0.396 mm 2 , and the total surface area of the first bumps is about 0.117 mm 2 . Thus, the total surface area of the first bumps is about 30% of the surface area of the first electrode. The surface area of the second electrode  56  is about 0.089 mm 2 , and the total surface area of the second bumps is about 0.048 mm 2 . Thus, the total surface area of the second bumps is about 54% of the surface area of the second electrode. 
     As a comparative example, as shown in  FIG. 5 , a light emitting device was prepared using a light emitting element  60  having 6×1 pieces of second bumps  66  as opposed to the light emitting element  20 . The light emitting device of the comparative example has a similar construction to that of Example 1 except for having no first small bumps and a fewer number of second bumps  66 . 
     Evaluation 
     The thermal resistance and the bump strength of the light emitting devices of Example 1 and the comparative example were measured. 
     The results show that the thermal resistance (° C./W) decreased by 6.5% and the bonding strength (gf) between the light emitting element and the substrate increased by 4.5% as compared to the comparative example. 
     The light emitting device according to the present invention can be used as a light source in various applications, such as for lighting fixtures, various indicators, automotive lights, displays, liquid crystal display backlights, sensors, traffic lights, automotive parts, signage channel letters, and the like.