Patent Publication Number: US-2013249387-A1

Title: Light-emitting diodes, packages, and methods of making

Description:
BACKGROUND 
     The present embodiments relate to light-emitting diodes (LEDs), packages including LEDs, and methods of making LED packages. 
     DESCRIPTION OF RELATED ART 
     Light Emitting Diodes (LEDs), or laser diodes, are widely used for many applications. A semiconductor light emitting device includes an LED chip having one or more semiconductor layers. The layers are configured to emit coherent and/or incoherent light when energized. During manufacture, a large number of LED semiconductor dies are produced on a semiconductor wafer. The wafer is probed and tested to accurately identify particular color characteristics of each die, such as color temperature. Then, the wafer is singulated to cut the wafer into a plurality of chips. The LED chips are typically packaged to provide external electrical connections, heat sinking, lenses or waveguides, environmental protection, and/or other features. Conventional methods for making LED chip packages comprise processes such as die attach, wire bonding, encapsulating, testing, etc. 
     It is often desirable to incorporate a phosphor into the LED package, to enhance the emitted radiation in a particular frequency band and/or to convert at least some of the radiation to another frequency band. Conventionally, phosphors are included during the LED chip packaging process. In one technique, the phosphor may be suspended in the encapsulant provided in the LED package. In an alternative approach, the phosphor may be directly coated on the LED chip, after the steps of die attach and wire bonding, by dispensing or spray coating. 
     However, in the dispensing method it is difficult to control the thickness of phosphor. Variations in the phosphor thickness create color non-uniformity of the light output from the LED package. The spray coating method provides better thickness control, but is expensive due to phosphor waste, since the phosphor sometimes coats portions of the work piece other than those desired to be coated. 
     After the phosphor is added, another test may be performed to determine whether the light emission of the packaged LED chip with phosphor conforms to a desired color characteristic, such as color temperature. Any unsatisfactory packages may be discarded or reworked. Reworking typically involves manual removal of excessive phosphor or manual addition of extra phosphor to make up for a phosphor deficiency. Manual processes significantly increase manufacturing costs. 
     It has been proposed to apply a phosphor coating on a semiconductor LED wafer while exposing each die&#39;s bonding pads via a photopatternable film or by stencil printing. However, the photopatternable film requires an expensive photomask. Stencil printing does not allow selectively coating a very thin, typically under 100 μm, phosphor layer, which includes phosphor particles having a diameter of 5-15 μm. 
     SUMMARY 
     The various embodiments of the present light-emitting diodes, packages, and methods of making have several features, no single one of which is solely responsible for their desirable attributes. Without limiting the scope of the present embodiments as expressed by the claims that follow, their more prominent features now will be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description,” one will understand how the features of the present embodiments provide the advantages described herein. 
     One aspect of the present embodiments includes the realization that it would be beneficial to have a simple and efficient way to selectively apply a phosphor coating on a semiconductor wafer, while allowing for wafer level color testing before proceeding to singulation and chip packaging. 
     One of the present embodiments comprises a light-emitting diode (LED) element. The LED element comprises an LED chip having a light emitting surface and at least one pad. The LED element further comprises a phosphor layer formed on the light emitting surface and exposing the at least one pad. The phosphor layer includes a plurality of phosphor particles and a matrix. At least some of the phosphor particles have a first portion embedded in the matrix and a second portion protruding from an outer surface of the matrix. 
     Another of the present embodiments comprises a light-emitting diode (LED) package. The LED package comprises a substrate and an LED element disposed on the substrate. The LED element comprises an LED chip having a light emitting surface and at least one pad. The LED element further comprises a phosphor layer formed on the light emitting surface and exposing the at least one pad. The phosphor layer includes a plurality of phosphor particles and a matrix. At least some of the phosphor particles have a first portion embedded in the matrix and a second portion protruding from an outer surface of the matrix. The LED package further comprises at least one electrical element electrically connecting the at least one pad of the LED chip to the substrate. The LED package further comprises an encapsulant encapsulating the LED chip and the electrical at least one electrical element. 
     Another of the present embodiments comprises a method of making a chip having a first surface and a plurality of pads disposed on the first surface. The method comprises providing a temporary substrate including a bonding surface and a plurality of protruding portions on the bonding surface. Locations of the protruding portions on the temporary substrate correspond to locations of the pads on the first surface of the chip. The method further comprises forming an adhesive layer on each of the protruding portions. The method further comprises bonding the temporary substrate to the chip such that the protruding portions are connected to respective ones of the pads via the adhesive layers. The bonding surface of the temporary substrate faces the first surface of the chip and a dispensing space is formed between the bonding surface and the first surface. The method further comprises filling the dispensing space with a glue to form a gel layer encapsulating the pads, the protruding portions. and the adhesive layers. The method further comprises removing the temporary substrate to separate the protruding portions and the adhesive layers from the pads to form a plurality of openings in the gel layer, the openings exposing respective ones of the pads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 4  is a cross-sectional side view of an LED package according to the present embodiments; 
         FIGS. 2A-2I  are schematic cross-sectional views illustrating steps in one embodiment of a method of making the LED package of  FIG. 4 ; 
         FIGS. 3A and 3B  are schematic cross-sectional views illustrating steps in a method of making a phosphor layer according to the present embodiments; 
         FIG. 4  is a cross-sectional side view of another LED package according to the present embodiments; 
         FIGS. 5A-5I  are schematic cross-sectional views illustrating steps in a dispensing method according to the present embodiments; and 
         FIGS. 6A-6F  are schematic cross-sectional views illustrating steps in another dispensing method according to the present embodiments. 
     
    
    
     Common reference numerals are used throughout the drawings and the detailed description to indicate the same elements. The present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a cross-sectional view of a light-emitting diode (LED) package according to one of the present embodiments is illustrated. The LED package  100  includes a substrate  110 , an LED element  120 , a plurality of electrical elements  130 , and an encapsulant  140 . The LED element  120  comprises an LED chip  121  and a phosphor layer  122 . 
     The LED chip  121  can comprise a light-emitting diode, a laser diode, or another device that may include one or more semiconductor layers. The semiconductor layers may comprise silicon, silicon carbide, gallium nitride, or any other semiconductor materials. The LED chip  121  may further comprise a substrate (not shown), which may be sapphire, silicon, silicon carbide, gallium nitride, or any other material. The LED chip  121  may further comprise one or more contact layers (not shown), which may comprise metal or any other conductive material. 
     The substrate  110  comprises an upper surface  110   u  having at least one electrical contact  111 . The substrate may be a silicon interposer, a ceramic substrate. a printed circuit board, or any other type of substrate. The electrical contacts  111  may be pads, or any other type of contacts. 
     The LED chip  121  is disposed on the upper surface  110   u  of the substrate  110 . In the illustrated embodiment, the LED chip  121  is disposed on the substrate  110  in a face-up manner and electrically connected to the substrate  110  with wires  130 . The LED chip  121  has a light-emitting surface  121   u,  and comprises a plurality of pads  1211 , each having an upper surface  1211   u  (inset A′ in  FIG. 1 ). 
     The phosphor layer  122  is formed on the light emitting surface  121   u.  The phosphor layer  122  has a plurality of cavities  122   a  that expose a plurality of pads  1211 . In the illustrated embodiment, the phosphor layer  122  projects above upper surfaces  1211   u  of the pads  1211  (detail view A′ of  FIG. 1 ). The phosphor layer  122  comprises a plurality of phosphor particles  1221  suspended in a matrix  1222 . Materials for the matrix maybe transparent resins such as transparent silicone. Preferably, the phosphor particles  1221  are substantially uniformly distributed in the matrix  1222 , so that the LED package  100  has excellent color consistency. 
     Many of the phosphor particles  1221  are completely embedded in the matrix  1222 . However, as illustrated in A′ of  FIG. 1 , some phosphor particles  1221  located on an outer periphery of the matrix  1222  are only partially embedded. These partially embedded phosphor particles  1221  have a portion embedded in the matrix  1222  and another portion protruding from an outer surface  122   s  of the matrix  1222 , thereby giving the outer surface  122   s  a rough texture which, in certain package types (such as air cavity package) having only air or gas filled between the phosphor layer and the light output surface (such as a transparent cover&#39;s surface), can increase the overall light-emitting efficiency by reducing the internal reflection on the interface between the phosphor layer and the air or gas. 
     The phosphor particles  1221  may enhance the LED chip  121 &#39;s emitted radiation in a particular frequency band and/or convert at least some of the emitted radiation to another frequency band. In one embodiment, the LED chip  121  may emit blue light and the phosphor particles  1221  may comprise Cerium doped Yttrium Aluminum Garnet (YAG:Ce) (e.g., (YGdTb) 3 (AlGa) 5 O 12 :Ce) which can convert part of the blue light into yellow light, producing white light. 
     Alternatively, the phosphor particles  1221  may comprise (SrBaCaMg) 2 SiO 4 :Eu, (Sr,Ba,CaMg) 3 SiO 5 :Eu, CaAlSiN 3 :Eu, CaScO 4 :Ce, Ca 10 (PO 4 )FCl:SbMn, M 5 (PO 4 ) 3 Cl:Eu, BaBg 2 Al 16 O 27 :Eu, Ba, MgAl 16 O 27 :Eu, Mn, 3.5 MgO.0.5 MgF 2 .GeO 2 :Mn, Y 2 O 2 S:Eu, Mg 6 As 2 O 11 :Mn, Sr 4 Al 14 O 25 :Eu, (Zn,Cd)S:Cu, SrAl 2 O 4 :Eu, Ca 10 (PO 4 ) 6 ClBr:Mn, Eu, Zn 2 GeO 4 :Mn, Gd 2 O 2 S:Eu or La 2 O 2 S:Eu, wherein, M is an alkali earth metal, e.g., Sr, Ca, Ba, Mg, or a combination thereof In certain embodiments, sizes of the phosphor particles  1221  may range between about 5-20 μm. 
     With reference to the detail view A′ of  FIG. 1 , the outer surface of the phosphor layer  122  comprises an upper surface  122   s   1  and a lateral surface  122   s   2  extending between the upper surface  122   s   1  and the pads  1211 . In the illustrated embodiment, the lateral surface  122   s   2  is inclined, such that each cavity  122   a  has a top opening in the upper surface  122   s   1  and the top opening is larger than the corresponding pad&#39;s surface. In other embodiments, the lateral surface  122   s   2  could be vertical so that the width of each cavity  122   a  is constant over its height. 
     With reference to  FIG. 1 , a peripheral portion  122   p  of the phosphor layer  122  has a first lateral edge surface  122   s   3 , and the LED chip  121  has a second lateral edge surface  121   s.  The first lateral edge surface  122   s   3  and the second lateral edge surface  121   s  together define the edge surface of the LED chip  121 . In the illustrated embodiment, the first lateral edge surface  122   s   3  and the second lateral edge surface  121   s  are coplanar, but in other embodiments they may not be. 
     With continued reference to  FIG. 1 , the encapsulant  140  encapsulates the LED chip  121  and the electrical elements  130 . The encapsulant  140  comprises a first portion  141  and a second portion  142 . The first portion  141  covers a periphery of the upper surface  110   u  of the substrate  110 , and is shaped as a ring. The second portion  142  extends inward and upward from the first portion  141 , and is shaped as a dome. In other embodiments, the first and second portions  141 ,  142  could have other shapes. In particular, the second portion  142  could be angular. 
     The matrix  1222  and the encapsulant  140  may be the same material or different materials. For example, one or both may be a transparent polymer or translucent polymer, such as epoxy-based resin, a mixture thereof or any other suitable encapsulating agent. In one embodiment, the matrix  1222  or the encapsulant  140  may comprise an organic filler or an inorganic filler, such as, SiO 2 , TiO 2 , Al 2 O 3 , Y 2 O 3 , carbon black, sintered diamond powder, asbestos, glass, or a combination thereof. 
     A method of making a phosphor layer according to one of the present embodiments is described below with reference to  FIGS. 2A-2E .  FIG. 2A  illustrates an LED wafer  121 ′ including a plurality of non-singulated LED chips  121 . Each chip  121  includes the upper light emitting surface  121   u  and at least one of the pads  1211 . As illustrated in  FIG. 2B , a phosphor material  122 ″ is formed over the light emitting surface  121   u  and the pads  1211  of each LED chip  121 . The phosphor material  122 ″ may be formed by dispensing or printing, for example, or by any other technique. 
     Then, with reference to  FIG. 2C , the phosphor material  122 ′ is stamped with a micro-imprint mold  150  to form a stamping pattern. Specifically, the micro-imprint mold  150  comprises a plurality of protrusions  151  projecting from its lower surface  1501 . Positions of the protrusions  151  correspond to positions of the pads  1211 . After stamping, a thickness D 1  of first portions  1221 ′ of the phosphor material  122 ′ between the protrusions  151  and the pads  1211  is less than a thickness of second portions  1222 ′ positioned laterally of the pads  1211 . Thus, in a subsequent etching process, and without the need for a mask, the first portions  1221 ′ of the phosphor material  122 ′ can be completely removed while the second portions  1222 ′ remain. This etching process is discussed further below with respect to  FIG. 2D . 
     In one embodiment, the phosphor material  122 ′ may be cured during the stamping process to avoid sedimentation of the phosphor particles  1221  in the phosphor material  122  which, in turn, results in a non-uniform distribution of the phosphor particles  1221  in the phosphor material  122 ′. As discussed above, a uniform distribution of the phosphor particles  1221  in the phosphor material  122 ′ facilitates the light emitting color of the LED package  100  falling within the expected bin of the CIE coordinate system. 
     The phosphor material  122 ′ may be cured by any technique, such as heating the micro-imprint mold  150  to generate heat H transferred to the phosphor material  122  via the micro-imprint mold  150 . Alternatively, the micro-imprint mold  150  may comprise a heating element (not illustrated), which provides the heat to the phosphor material  122 ′. 
     With reference to  FIG. 2D , an etching process removes the first portions  1221 ′ ( FIG. 2C ) of the phosphor material  122 ′. This etching process may be performed without a mask over the second portions  1222 ′ ( FIG. 2C ). Even without a mask, the first portions  1221 ′ are completely removed to form the cavities  122   a  that expose the pads  1211 , while the second portions  1222 ′ remain on the LED wafer  121 ′. Referring back to  FIG. 2C , this result is due to the thickness Dl of the second portions  1222 ′ being larger than that of the first portions  1221 ′. Performing etching without a mask lowers manufacturing costs, because a mask need not be prepared. 
     In certain embodiments, the step of removing the first portions  1221 ′ may include an etching process and a residual particles cleaning process. The etching process may be a reactive ion etching (RIE) process. In some embodiments, the phosphor material  122 ′ may be etched by a wet etching process or other suitable etching process. In addition, a plasma atmosphere adopted in certain etching processes may be oxygen mixed with trifluoromethane (O 2 +CHF 3 ) or oxygen mixed with tetrafluoromethane (OH 2 +CF 4 ). A residual particles cleaning process may comprise washing the phosphor layer  122  with, for example, deionized water, to remove any detached phosphor particles  1221  and any residual etching agent. 
     With reference to FIG.  1 A′, in the etching process the matrix material  1222 ′ at the outermost extent of the phosphor material  122 ′ is removed, such that some phosphor particles  1221  become partially exposed. The partially exposed phosphor particles  1221  form the rough outer surface  122   s  described above. The outer surface  122   s  may achieve different degrees of roughness by controlling the proportions of plasma gases in the etching process, for example. 
     As discussed above, the lateral surface  122   s   2  of the phosphor material  122 ′ may be inclined or sloped after being etched, but could instead be substantially perpendicular to the upper surface  1211   u  of the pads  1211 . By properly controlling the manufacturing process, or adopting other etching process(es), the lateral surface  122   s   2  of the phosphor material  122 ′ can be given any desired orientation. 
     With reference to  FIG. 2E , the LED wafer  121 ′ and the phosphor layer  122  are singulated to form a plurality of LED elements  120  having a phosphor layer  122  formed on an LED chip  121 . The slits S 1  generated by the singulation process form the first lateral edge surface  122   s   3  of the matrix  1222 , and the second lateral edge surface  121   s  of the LED chip  121 . Again, the surfaces  122   s   3 ,  121   s  are substantially coplanar. In certain embodiments, the slits S 1  may be formed by a laser or a cutting tool. 
     Note that, before conducting the singulation step, the wafer  121 ′ shown in  FIG. 2D  is probed and tested to accurately identify each die&#39;s color characteristic. Typically, a color chart is used to associates two parameters (X and Y) with the color characteristic, i.e., the color temperature and a number of bins each including a range of X and Y values are defined in the color chart. The color chart provides a mechanism by which the X and Y values can be used to accurately identify particular colors for the purpose of binning and sorting the dies with phosphor coating thereon as described here. During the probing process, a probing device includes contacts points that are positioned to touch the pads  1211  of each die. The pads  1211  are exposed and accessible through the cavities  122   a.  Once the dies are energized, the probing device measures color temperature, lumen output, voltage, current, and any other operating parameters associated with each die. In an aspect, the measured parameters for each die are mapped to X and Y values based on the color chart. Thus, each die is associated with its own X and Y values prior to singulation. Thus, as each die is separate from the wafer during the singulation process, its associated X and Y value can be used to sort it into the appropriate bin. The dies with phosphor coating thereon in each bin can then be packaged using any packaging method to produce LED packages having excellent color consistency. 
     A method of packaging an LED chip  121  having a phosphor layer  122  according to one of the present embodiments is described below with reference to  FIGS. 2F-2I . With reference to  FIG. 2F , an LED chip  121  having a phosphor layer  122  is disposed on a substrate  110 . The substrate  110  comprises a plurality of electrical contacts  111 , such as pads. With reference to  FIG. 2G , the pads  1211  of the LED chip  121  and the electrical contacts  111  of the substrate  110  are electrically connected by a plurality of electrical elements  130 . In this embodiment, the LED chip  121  is disposed on the substrate  110  in a face-up orientation, and the electrical elements  130 , which may be solder wires, for example, connect the LED chip  121  and the substrate  110 . 
     With reference to  FIG. 2H , the LED chip  121  and the electrical elements  130  are encapsulated by an encapsulant  140 , which also covers the upper surface  110   u  of the substrate  110 . With reference to  FIG. 21 , slits S 2  are formed passing through the encapsulant  140  and the substrate  110  to form a plurality of the LED packages  100  illustrated in  FIG. 1 . In certain embodiments, the slits S 1  may be formed by a laser or a cutting tool. 
     In the above embodiment, the phosphor material  122 ′ ( FIG. 2B ) is formed on the LED wafer  121 ′ before the stamping process is performed ( FIG. 2C ). However, the phosphor material  122 ′ may be formed on the micro-imprint mold  150  before the stamping process is performed, as described below. 
     A method of making a phosphor layer according to another of the present embodiments is described below with reference to  FIGS. 3A and 3B . With reference to  FIG. 3A , the phosphor material  122 ′ may be directly formed on the micro-imprint mold  150  such that the phosphor material  122 ′ covers the protrusions  151 . With reference to  FIG. 3B , the phosphor material  122 ′ is then stamped onto the light emitting surface  121   u  of the LED chip  121  with the micro-imprint mold  150 . In this embodiment, the phosphor layer may thus be formed by transfer printing. 
     Referring to  FIG. 4 , a cross-sectional view of a light-emitting diode (LED) package  102  according to another of the present embodiments is illustrated. The package  102  includes an LED chip  121  disposed on a substrate  110 , and a gel layer  160  disposed on the LED chip  121 . The substrate may be, for example, a silicon substrate, a ceramic substrate or a printed circuit board. 
     The LED chip  121  includes a first, light-emitting surface  121   u  and a plurality of bonding pads  144  disposed on the first surface  121   u.  The bonding pads  144  of the LED chip  121  are connected to the substrate&#39;s pads  152  via electrical components  170 , such as bonding wires. The gel layer  160  covers the first surface  121   u,  and includes a plurality of openings  164  exposing respective ones of the bonding pads  144 . Each opening  164  includes a draft angle α, which results from the removal of a mold during a process of making the package  102 , as described below. The draft angle α may be between about 3° and about 20° to facilitate easy removal of the mold while preserving a substantially uniform thickness of the gel layer  160 . In certain embodiments, the draft angle α may be between about 5° and about 10°. 
     Materials for forming the gel layer  160  include, without limitation, transparent resins, such as transparent silicone. In addition, the gel layer  160  may include a plurality of phosphor particles  162 . The diameter of the phosphor particles  162  may be between about 5 μm and about 20 μm. The phosphor particles  162  may enhance the LED chip&#39;s emitted radiation in a particular frequency band and/or convert at least some of the emitted radiation to another frequency band. Materials for forming the phosphor particles  162  may comprise any of those described above with reference to the phosphor particles  1221 , or other materials. 
     With further reference to  FIG. 4 , an encapsulant  180  encapsulates the LED chip  121  and the electrical components  170 . The illustrated profile shape of the encapsulant  180  is only one example, and could be any shape. The encapsulant  180  may comprise transparent polymers or translucent polymers, such as glass cement, elastomer or resins, wherein resins comprises epoxy-based resins, silicone-based resins, mixtures of epoxy-based resins and silicone-based resins, or other materials. In certain embodiments, the encapsulant  180  may be mixed with organic or inorganic fillers, such as silicon dioxide, titanium dioxide, aluminum oxide, iridium oxide, carbon black, sintered diamond powder, asbestos, glass, and/or combinations thereof. 
     A method of forming the gel layer  160  on the LED chip  121  according to one of the present embodiments is described below with reference to  FIGS. 5A-5I .  FIG. 5A  illustrates a temporary substrate  113 . The temporary substrate includes a bonding surface  112  and a plurality of protruding portions  114  (only two shown in  FIG. 5A ) located on the bonding surface. In this embodiment, the side wall of each protruding portion  114  has a slant angle β which may be between about 2° and about 19°. In certain embodiments, the slant angle β may be between about 4° and about 9°. The material of the protruding portions  114  may be, for example, a metal. 
     With reference to  FIG. 5B , a release layer  124  is provided on the temporary substrate  113 . The release layer covers the bonding surface  112  and the protruding portions  114  and facilitates easy removal of the temporary substrate  113  later in the present process. The release layer  124 , which may comprise fluoropolymers, for example, may be formed by spraying or dipping, for example. 
     With reference to  FIG. 5C , portions of the release layer  124  that cover a bonding area  114   a  of each bump  114  are removed to expose the bonding areas  114   a.  Then, with reference to  FIG. 5D , an adhesive layer  131  is formed on the bonding area  114   a  of each of the protruding portions  114 . The adhesive layers  131  may be, for example, an ultraviolet-curable adhesive or a double-sided tape. In order to facilitate removal of the temporary substrate  113 , the bond strength of the ultraviolet-curable adhesive can be reduced by UV curing prior to removing the temporary substrate  113 . The double-sided tape may have greater bond strength on a first side that adheres to the temporary substrate  113  than on a second side that adheres to the protruding portions  114 . 
     Next, with reference to  FIG. 5E , the temporary substrate  113  is located above the LED chip  121  disposed on the substrate  110 . This step may be performed by a pick and place machine, for example. The protruding portions  114  of the temporary substrate  113  are located at positions corresponding to locations of the bonding pads  144  of the LED chip  121 . 
     Next, with reference to  FIG. 5F , the temporary substrate  113  is bonded to the LED chip  121 , so that the protruding portions  114  are connected to respective ones of the bonding pads  144  of the LED chip  121  via the adhesive layers  131 . At this point, the bonding surface  112  of the temporary substrate  113  faces the first surface  121  u of the LED chip  121 , and a dispensing space S is formed between the bonding surface  112  and the first surface  121   u.  If the adhesive layers  131  are double-sided tape, the bond strength between the double-sided tape and the protruding portions  114  of the temporary substrate  113  is preferably greater than the bond strength between the double-sided tape and the bonding pads  144  of the LED chip  121 . In certain embodiments, a distance D between the bonding surface  112  of the temporary substrate  113  and the first surface  121   u  of the LED chip  121  is, for example, greater than 50 μm and less than 100 μm. 
     Next, with reference to  FIGS. 5G and 5H , the dispensing space S is filled with a glue  160   a.  The temporary substrate  113  together with the protruding portions  114  and the adhesive layers  131  acts as a mold to shape the filled glue such that no glue comes into contact with the bonding pads  144 , thereby facilitating high-quality wire bonds (described below). The glue  160   a  can be provided by a dispenser  10  or a nozzle (not shown) to an edge of the dispensing space S. Due to the small gap between the bonding surface  112  of the temporary substrate  113  and the first surface  121   u  of the LED chip  121 , capillary action draws the glue  160   a  into the dispensing space S in the direction of the arrow A. A viscosity of the glue  160   a  may be between about 3,000 cP and 20,000 cP. 
     Subsequently, with reference to  FIGS. 5H and 5I , the temporary substrate  113  together with the protruding portions  114  and the adhesive layers  131  are separated from the bonding pads  144 , thereby forming a plurality of openings  164  in the gel layer  160 . The presence of the release layer  124  on the temporary substrate  113  facilitates easier separation of the protruding portions  114  and the adhesive layers  131  from the bonding pads  144 . If the adhesive layers  131  are ultraviolet-curable adhesives. UV irradiation may be applied to the adhesive layers  131  before removing the temporary substrate  110  to reduce the bond strength between the adhesive layers  131  and the bonding pads  144 . 
     After filling the dispensing space S, the glue  160   a  is cured to form the gel layer  160 . The curing process may comprise a pre-curing step performed when the temporary substrate  113  is attached to the chip  121  and a post-curing step performed after the temporary substrate  113  is separated from the chip  121 . The curing process may be performed by any technique, such as using a heating element (not illustrated) to provide the heat to the glue  160   a.    
     The openings  164  expose respective ones of the bonding pads  144  of the LED chip  121 . The draft angle α of each opening  164  is slightly larger than the slant angle β of the side wall of the corresponding bump  114  since the glue  160   a  contracts slightly during the curing process. At this point, the dispensing method has formed the gel layer  160  on the LED chip  121 . 
     In the present embodiments, since a substantially constant distance D separates the bonding surface  112  of the temporary substrate and the first surface  121   u  of the LED chip  121 , the thickness of the gel layer  160  can be closely controlled. Furthermore, since the Gel layer  160  can be easily confined in the gap between the bonding surface  112  and the first surface  121   u,  little if any glue material  160   a  is wasted. In conventional spray-coating methods, a large quantity of glue is wasted, since it is deposited on the substrate in addition to the LED chip. 
     With reference to  FIG. 6A , any or all of the steps of the foregoing dispensing method can be performed on a wafer  200  including a plurality of chips  210 . For example,  FIG. 6A  illustrates a temporary substrate  113   a,  which is, for example, a wafer level substrate corresponding to the wafer  200 . The temporary substrate  113   a  includes a bonding surface  112   a  and a plurality of protruding portions  114  located on the bonding surface  112   a.  An adhesive layer  131  is formed on a bonding area  114   a  of each of the protruding portions  114 . Next, the temporary substrate  113   a  is bonded to the wafer  200  disposed on a carrying board  250 , so that the protruding portions  114  connect to respective ones of the pads  204  of the wafer  200  via the adhesive layers  131 . At this point, the bonding surface  112   a  of the temporary substrate  113   a  faces the top surface  202  of the wafer  200 , and a dispensing space S′ is formed between the bonding surface  112   a  and the top surface  202 . Next, with reference to  FIGS. 6B and 6C , the dispensing space S′ is filled with a glue  160   a.  The glue  160   a  can be provided by a dispenser  10  or a nozzle (not shown) to an edge of the dispensing space S. Due to the small gap between the bonding surface  112   a  of the temporary substrate  113   a  and the top surface  202  of the wafer  200 , capillary action draws the glue  160   a  into the dispensing space S′ in the direction of the arrow A to form the gel layer  160 . The gel layer  160  encapsulates the pads  204 , the protruding portions  114 , and the adhesive layers  131 . In addition, the glue  160   a  can include a plurality of phosphor particles  162 . 
     Subsequently, with reference to  FIGS. 6C and 6D , the temporary substrate  113   a  is removed, so that the protruding portions  114  and the adhesive layers  131  are separated from the pads  204  to form a plurality of openings  164  in the gel layer  160 . The openings  164  expose respective ones of the pads  204  of the wafer  200 . Next, with reference to  FIG. 6E , after removing the temporary substrate  113   a,  the wafer  200  and the gel layer  160  are cut along the line L, to form independent chips  210 . With reference to  FIG. 6F , a side wall of the gel layer  160  and a side wall of the chips  210  are substantially coplanar. At this point, the gel layer  160  has been formed on the wafer  200  that includes multiple chips  210 . 
     While the invention has been described and illustrated with reference to specific embodiments thereof, these descriptions and illustrations do not limit the invention. It should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. The illustrations may not necessarily be drawn to scale. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus due to manufacturing processes and tolerances. There may be other embodiments of the present invention which are not specifically illustrated. The specification and the drawings are to be regarded as illustrative rather than restrictive. Modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.