Abstract:
Intermediate removable placement and processing structures are provided to enable the formation of optical elements upon light emitting elements, including the formation of a reflective layer beneath the optical elements. These removable placement and processing structures are substantially independent of the particular dimensions of the produced light emitting device, allowing their re-use in a variety of applications. The resultant light emitting device includes the light emitting element,the optical element with reflector, and, optionally, a wavelength conversion material, but does not include remnants of the placement and processing structures, such as a carrier substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of light emitting devices, and in particular to a light emitting device (LED) that is suitable for attachment to a printed circuit (PC) or other fixture, and includes an optical element, but does not include a substrate carrier. 
       BACKGROUND OF THE INVENTION 
       [0002]    The ever expanding use of semiconductor light emitting devices has produced a highly competitive market for these devices. In this market, performance and price are often significant for providing product distinction among vendors. 
         [0003]    One technique for reducing the cost of the device is to reduce material costs by reducing the number of components forming the device and/or using less costly components. Additionally or alternatively, the cost of the device may be reduced by reducing the manufacturing costs by reducing the number of manufacturing processes and/or using less costly manufacturing processes. 
         [0004]    One technique used to reduce manufacturing costs is to process multiple devices during each manufacturing step. However, the processing of multiple devices often requires the use of components that are provided primarily to accommodate the manufacturing process. 
         [0005]    In the manufacture of light emitting devices, hundreds of light emitting elements are produced/grown on a growth substrate, with minimal ‘wasted’ space between the light emitting elements. These light emitting elements are generally substantially smaller than the eventual size of the light emitting device, because the light emitting device generally requires an optical element that serves to provide a desired light output pattern and also serves to protect the light emitting element; the light emitting device may also include a wavelength conversion element to produce a composite multi-wavelength light output, such as white light. Accordingly, space must be provided between the light emitting elements that are to receive these additional components. 
         [0006]    To situate the light emitting elements at an appropriate spacing to allow the optical and other elements to be added to multiple light emitting elements during a single process, the growth substrate is sliced/diced to provide individual (‘singulated’) light emitting elements, and these light emitting elements are attached to a substrate carrier that is formed to create an array of appropriately spaced light emitting elements. The substrate carrier is generally also configured to facilitate subsequent mounting and packaging requirements, including providing external electrical contact to the light emitting elements. 
         [0007]    After the light emitting elements are mounted upon the substrate carrier, typically by soldering the contact pads of the light emitting element to conductors that provide for the external electrical contact on the substrate carrier, the optical elements and optional wavelength conversion elements are applied to the multiple light emitting elements on the substrate carrier. Thereafter, the substrate carrier is sliced/diced to provide the individual (‘singulated’) light emitting devices. 
         [0008]      FIGS. 3A-3B  illustrate a profile view and a top view of an example prior art singulated light emitting device  300 . The light emitting device  300  includes a light emitting element  320 , or chip, that is ‘flip-chip’ mounted upon a singulated portion of a substrate carrier  310 , conventionally termed a ‘submount’  310 . When the light emitting element  320  is formed on the growth substrate (not-shown), the semiconductor layers forming the light emitting element  320  are grown first, and the conductive layers forming the contact to the semiconductor layers are grown atop the semiconductor layers, with contact pads  330  at the uppermost layer. A flip-chip mounting provides the contact pads  330  on the lower surface of the light emitting element  320 , and the majority of light is emitted from the upper surface of the light emitting element  320 . In this example, the growth substrate upon which the light emitting element  320  had been grown has been removed, to increase the light output efficiency. 
         [0009]    The submount  310  includes conductors  340  that provide for external contact to contact pads  330  on the lower surface of the light emitting element  320 , and the contact pads  330  are attached to these conductors  340 , typically using a solder layer  335 . The submount  310  may also include reflective material (not shown) to redirect light away from the submount  310 . 
         [0010]    During the processing of the un-singulated substrate carrier, a wavelength conversion element  350  has been attached to each of light emitting elements  320 , and an optical element  360  has been applied above the wavelength conversional material  350 . Optionally, the wavelength conversion material, such as phosphor particles, may be included within the material used to form the optical element  360 , eliminating the need for separate applications of these elements  350 ,  360 . 
         [0011]    Upon singulation, the finished light emitting device  300  includes the submount  310 , the light emitting element  320 , the optical and wavelength conversion elements  350 ,  360 , and external connections  340  to the light emitting element. Of particular note, the submount  310  defines the overall dimensions of the finished light emitting device  300 . If a larger optical element is desired for a particular application, a different submount must be designed; if a smaller optical element is sufficient for a particular application, either a different submount must be designed, or a loss of useful area may be incurred. Additionally, some applications may require multiple light emitting devices in a particular arrangement, and the dimensions of the submount  310  may preclude the desired arrangement, again requiring the design of a different submount. 
         [0012]    Other techniques that do not use a submount, per se, are also commonly used to produce a packaged light emitting device. Leadframes and leadframe carriers are commonly used to facilitate the manufacture of multiple light emitting devices during each process. 
         [0013]    A leadframe is generally a conductive structure that provides contacts (leads) for externally connecting to a light emitting element. The two contact pads on the light emitting element are soldered to the ends of two leads that extend away from the light emitting element. The leads may be shaped and bent to situate the opposite ends of the leads in the appropriate location and orientation for subsequent mounting on a printed circuit board or other fixture. 
         [0014]    The leadframe carrier comprises multiple leadframes, and allows for subsequent processing of multiple light emitting elements on the leadframe carrier. For example, optical elements may be molded over the leadframe carrier before the individual light emitting elements on leadframes are singulated. Typically, the molded element extends beneath the surface of the leads upon which the light emitting element is soldered, effectively forming a substrate carrier comprising molded material and conductors (leads) beneath the light emitting element. 
         [0015]    As in the above example of a submount, the formed substrate carrier about each leadframe with light emitting element effectively defines the dimensions of the finished product. If more or less space is required between leadframes on a leadframe carrier to accommodate larger or smaller optical elements, a new leadframe carrier is likely to be required. 
         [0016]    In each of these examples, one of the primary functions of the substrate carrier is to provide a structure that allows for the placement and processing of multiple singulated light emitting elements, and in particular, to facilitate the formation of an optical element above each singulated light emitting element. Another primary function of the substrate carrier is to provide a reflective surface that redirects light into the optical element for emission from the light emitting device. 
       SUMMARY OF THE INVENTION 
       [0017]    It would be advantageous to provide a method of producing multiple light emitting devices that include a light emitting element and an optical element but do not include a substrate carrier. It would also be advantageous to provide a method of producing light emitting devices of different dimensions without requiring different components to accommodate the different dimensions. 
         [0018]    To better address one or more of these concerns, in an embodiment of this invention, intermediate removable placement and processing structures are provided to enable the formation of optical elements upon the light emitting element, including the formation of a reflective layer beneath the optical elements. These removable placement and processing structures are substantially independent of the particular dimensions of the produced light emitting device, allowing their re-use in a variety of applications. The resultant light emitting device includes the light emitting element, the optical element with reflector, and, optionally, a wavelength conversion material, but does not include remnants of the placement and processing structures, such as a carrier substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: 
           [0020]      FIGS. 1A-1F  illustrate an example process for forming a light emitting element with a wavelength conversion element. 
           [0021]      FIGS. 2A-2F  illustrate an example process for forming a light emitting device with a light emitting element and an optical element, without a carrier substrate. 
           [0022]      FIGS. 3A-3B  illustrate an example prior art light emitting device with a light emitting element, an optical element, and a carrier substrate element. 
       
    
    
       [0023]    Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention. 
       DETAILED DESCRIPTION 
       [0024]    In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. 
         [0025]      FIGS. 1A-1F  illustrate an example process for forming a light emitting element with a wavelength conversion element. 
         [0026]      FIG. 1A  illustrates the forming/growing of multiple light emitting elements  120  upon a growth substrate  110 . Each light emitting element  120  may typically include an active light emitting regions sandwiched between an N-type semiconductor region and a P-type semiconductor region. Conductive structures (not shown) are created during the formation of the light emitting elements  120  so as to provide contact pads  130  on the top-most layer of the light emitting element  120 . In some embodiments, the contact pads  130  may be on opposite surfaces of the light emitting element  120 . Individual light emitting structures  10  are formed by slicing/dicing  101  the growth substrate  110  with light emitting elements  120  to form individual (singulated) light emitting structures  10 . 
         [0027]      FIG. 1B  illustrate the placement of the light emitting structures  10  on an intermediate, removable structure  140 , such as a removable ‘sawing tape’ with an adhesive surface. As illustrated, the structures  10  are placed on the tape  140  in a ‘flip-chip’ orientation, with the contact pads  130  on the tape  140 , and the growth substrate  110  above the light emitting element  120 . In this example embodiment, the growth substrate  110  is not removed, and provides structural support and protection for the light emitting element  120 , thereby allowing for the structure  10  to be subsequently processed without being attached to a carrier substrate, as in the example of  FIGS. 3A-3B . 
         [0028]    Other means for providing structural support to the light emitting element  120  may also be used. For example, copending U.S. patent application 61/656,691, “CHIP SCALE LIGHT EMITTING DEVICE WITH METAL PILLARS IN A MOLDING COMPOUND FORMED AT WAFER LEVEL”, filed 7 Jun. 2012, for Jipu Lei, Stefano Schiaffino, Alexander Nickel, Mooi Guan Ng, Grigoriy Basin, and Sal Akram, (Attorney docket 2012PF00450) discloses that the conductor layers that form the connections between the contact pads  130  and the light emitting element  120  may be formed as thick metal pillars with dielectric material between the pillars, the encased pillars allowing the structure to be self-supporting. 
         [0029]    To enhance light output efficiency through the growth substrate  110 , the interface between the growth substrate  110  and the light emitting surface of the light emitting element  120  may be textured to reduce the amount of light that is totally internally reflected (TIR) at the interface. In an example embodiment, the growth substrate  110  may be a “Patterned Sapphire Substrate” (PSS) that allows the light emitting element  120  to be grown upon a patterned/textured surface of the growth substrate. 
         [0030]    In this example embodiment, the light emitting structures  10  are spaced apart sufficiently to allow for a wavelength conversion material  150  to be applied to the top and sides of the light emitting structure  10 , as illustrated in  FIGS. 1C-1D . To enhance the light extraction efficiency, the upper surface  115  of the growth substrate  110  may be textured/roughened to reduce total internal reflections at the interface between the wavelength conversion material  150  and the growth substrate  110 . Additionally (not illustrated), a layer of reflective material may be applied between the light emitting structures  10 , to reflect any downward traveling light in an upward direction, as detailed further with regard to  FIGS. 2A-2F . 
         [0031]    In the example of  FIG. 1C , a preformed laminate sheet of wavelength conversion material  150  is placed atop the light emitting structures  10 , then processed to conform to the shape of the spaced apart structures  10  on the tape  140 , as illustrated in  FIG. 1D . In an example embodiment, a combination of vacuum and heat is used to laminate the wavelength conversion material  150  to the light emitting structures  10 , such as disclosed in U.S. Pat. No. 7,344,952 issued to Haryanto Chandra on 18 Mar. 2008, and incorporated by reference herein. 
         [0032]    If the light emitting structures  10  are pre-tested and sorted (‘binned’) by their light output characteristics, structures  10  with similar characteristics can be placed on the tape  140 , and the preformed wavelength conversion sheet  150  may be selected such that its characteristics in conjunction with the light output characteristics of the light emitting structures  10  on the tape provide a desired composite light output. 
         [0033]    One of skill in the art will recognize that the wavelength conversion material  150  need not be in the form of a laminate sheet; it may be applied in liquid or paste form via spray coating, molding, screen printing, and so on. 
         [0034]    The light emitting structures  10  with wavelength conversion material  150 , hereinafter termed ‘structures  20 ’ are subsequently singulated by slicing  145  the material  150  between the structures  20 , as illustrated in  FIGS. 1E . Each of the structures  20  may subsequently be removed from the tape  140  as illustrated in  FIG. 1F . 
         [0035]      FIGS. 2A-2F  illustrate an example process for forming a light emitting device with a light emitting element and an optical element with a reflective element, and without a carrier substrate. Typically, optical elements may be formed upon a light emitting device using a mold that forms the appropriate shape for achieving the desired optical effect. A silicone or other transparent material in a liquid or paste form may be used as the mold material, and, as noted above, this material may be infused with wavelength conversion material. 
         [0036]    To withstand the stress imposed by a molding process, the light emitting structures  20 , comprising a light emitting element  120 , a growth substrate  110 , and optional wavelength conversion material  150  are placed on a carrier substrate  210  that is sufficiently robust to support the light emitting structures  20  during this process. These structures  20  are situated on the carrier  210  with sufficient space between them to allow the formation of an optical element that surrounds each structure  20 . 
         [0037]    To facilitate an easy removal of the subsequently formed devices from the carrier  210 , a double-sided adhesive tape  220  may be used to attach the structures  20  to the upper surface  221  of the tape  220 , and the lower surface  222  of the tape  220  to the carrier  210 , as illustrated in  FIG. 2A . The tape  220  may include a thermal release coating on the surface  222  that is attached to the carrier  210 , so that upon completion of the molding process, the tape  220  can be removed from the carrier  210  by curing it for a short time at a temperature that allows separation of the tape  220  from the carrier  210 , allowing the carrier  210  to be reused. 
         [0038]    At  FIG. 2B , a dispenser  235  applies reflective material  230  to the spaces between the structures  20  on the tape  220 . This reflective material  230  will serve to redirect any light directed to the bottom of the subsequently formed light emitting device back toward the intended light emitting surface of the optical element (not illustrated in  FIG. 2B ). This reflective material  230  may be a polymer with a highly reflective filler, such as Ti 0   2 , which is applied in liquid or paste form, and is subsequently cured to form a smooth layer of this reflective material  230 , as illustrated in  FIG. 2C . 
         [0039]    Optionally, depending upon the shape and other characteristics of the optical element, the reflective material  230  may be omitted, relying on total internal reflection (TIR) at the lower surface of the optical element to redirect light directed to this surface back toward the intended light emitting surface of the optical element. In some applications, the surface upon which the light emitting device is to be mounted may be reflective, and the reflective material  230  may be omitted. 
         [0040]    At  FIG. 2D , an optical element  250  is formed over each light emitting structure  20 . In the example of  FIG. 2D , the optical element  250  is in the form of a hemisphere above each light emitting structure  20 , although any of a number of different shapes may be formed to achieve a particular light emission pattern, such as a collimated light emission pattern. To simplify manufacture, the mold material may be applied to the entire surface area of the carrier  210 , such that the molding process produces the individual optical elements  250  connected together by the molding material  255  in the remaining spaces between the light emitting structures  20 . Of particular note, the reflective material  230  lies below the optical elements  250  and the intervening material  255 , so that light that may be directed downward through the optical elements  250  is reflected upward. 
         [0041]    At  FIG. 2E , the individual light emitting devices  30 , comprising the light emitting structure  20 , the reflective material  230 , and the optical element  250 , are singulated by slicing  280  through the optical element  250 , reflective material  230 , and into the tape  220 , above the carrier  210 . This partial slicing allows for the unmarred carrier  210  to be reused for forming other sets of light emitting devices. 
         [0042]    After the partial slicing to singulate the light emitting devices  30 , the tape  220  is removed from the devices  30  and the carrier substrate  210 , forming individual light emitting devices  30  without elements of the carrier substrate  210 , as illustrated in  FIG. 2F . 
         [0043]    One of skill in the art will recognize that the carrier substrate  210  may be removed before singulating the light emitting devices  30 , leaving the devices  30  on the tape  220  for subsequent singulation. 
         [0044]    The formed light emitting device  30  includes a light emitting element  120 , a growth substrate element  110 , an optional wavelength conversion material  150 , and reflective material  230  below the optical element  250  and intervening material  255 . As noted above, reflective material may also be placed beneath the wavelength conversion material  150 . 
         [0045]    Of particular note, the overall size of the light emitting device  30  includes the area occupied by the optical element  250  and material  255 , and the amount of material  255  can be increased or decreased to provide a desired size or shape of the finished light emitting device  30 . For example, in an application that uses a variety of different light emitting devices, the individual devices may be sized and shaped to fit together in a jig-saw like fashion. 
         [0046]    The size and shape of the finished light emitting device  30  is defined by the mold used to create the optical elements  250  on the carrier  210  and/or by the slicing/trimming of the intervening material  255  between the light emitting structures  20 , and is not at all defined by the carrier substrate  210 . Alternatively stated, the same carrier substrate  210  may be used regardless of the size or shape of the device required to satisfy the criteria of a particular application for the device. 
         [0047]    Additionally, because the carrier substrate  210  is reusable, and not ‘consumed’ in the process of creating the light emitting device  30 , the cost of the substrate  210  is not a direct cost in the manufacture of each light emitting device  30 . The cost of this substrate  210  is shared among all of the devices that will ever use this substrate  210 , and thus the per-device cost of this substrate  210  is virtually infinitesimal. 
         [0048]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
         [0049]    For example, it is possible to operate the invention in an embodiment wherein multiple light emitting elements are included in each light emitting structure, or multiple light emitting structures are encapsulated by a single optical element. Because a different carrier substrate is not required for each different combination of light emitting elements or light emitting structures within each optical element, the techniques of this invention provide substantial flexibility in the design and configuration of light emitting devices for varied applications. 
         [0050]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.