Abstract:
A lens structure is pre-formed with features that facilitate accurate alignment of a light emitting chip within the lens structure. To ease manufacturing, the features include tapered walls that allow for easy insertion of the light emitting chip into the lens structure, the taper serving to accurately align the light emitting chip when the chip is fully inserted. The taper may include linearly sloped or curved walls, including complex shapes. An adhesive may be used to secure the light emitting chip to the lens structure. The light emitting chips may be picked-and-placed into an array of lens structures, or picked-and-placed onto a substrate that may be overlaid by the array of lens structures.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of light emitting devices, and in particular to a light emitting device that is formed by placing a self supporting light emitting element into a preformed lens having a cavity with sloped walls that facilitate insertion of the light emitting element into the lens and facilitate adhering the light emitting element to the lens. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional light emitting devices include a light emitting element, such as a light emitting diode chip (LED chip) mounted on a substrate and encased in a protective enclosure that may serve as an optical lens. The substrate provides the structural support required to facilitate handling of the light emitting device during subsequent processes, such as the mounting of the light emitting device on a printed circuit board. The protective enclosure may include a wavelength conversion material that converts at least a part of the light emitted from the light emitting chip to light of a different wavelength. 
         [0003]    The wavelength conversion material may alternatively be provided as a discrete element between the light emitting chip and the enclosure/lens. 
         [0004]    Common techniques for providing a light emitting device as described above include attaching the light emitting element to a wire frame substrate that serves to allow external power connections to the light emitting element, then encapsulating the light emitting element and the portion of the wire frame to which it is attached with a silicone mold. The wire frame may be part of a carrier that includes multiple frames for mounting light emitting elements, such that the encapsulation can be performed for all of the light emitting elements as a single molding process. 
         [0005]    In another embodiment, the light emitting element is mounted on a ceramic substrate that includes conductors to which the light emitting element is attached. U.S. Pat. No. 7,452,737, “MOLDED LENS OVER LED DIE”, issued 18 Nov. 2008 to Grigoriy Basin, Robert Scott West, and Paul S. Martin, discloses a ceramic substrate that accommodates multiple light emitting elements, and a mold that forms a lens element over each of the light emitting elements. The ceramic substrate may subsequently be sliced/diced to provide ‘singulated’ light emitting devices that include external connections to the light emitting element on the ceramic substrate. 
         [0006]    In another embodiment, the substrate includes cup-like cavities within which the light emitting elements are attached to conductors for coupling the light emitting element to a power source. The light emitting elements are encapsulated by filling the cavities with a low viscosity silicone and curing the silicone. The cavity may be shaped to provide a particular optical effect, and/or a mold may be used to form a desired lens structure above the cup. U.S. Pat. No. 7,214,116, “LIGHT-EMITTING DIODE AND METHOD FOR ITS PRODUCTION”, issued 8 May 2007 to Akira Takekuma, discloses placing a preformed lens atop the silicone within the cup. After curing the silicone, the substrate is diced to provide the singulated light emitting devices. 
         [0007]    Each of the above processes requires singulating the light emitting dies, mounting each die on the substrate, encapsulating the dies on the substrate, then slicing/dicing the substrate to singulate the completed light emitting devices. In addition to the additional manufacturing cost and effort associated with the double-handling involved with the intermediate step of mounting the light emitting dies on a substrate, this double-handling process also challenges applications wherein the light emitting die is required to have a particular location with respect to the optics of the enclosing structure. In many applications, if the light emitting element is ‘off-center’ relative to the optics of the enclosing structure, the formed light emitting device may be discarded as ‘failed’ in the manufacturing process, or may pass the manufacturing test and result in a defective product when it is incorporated into the product. For example, in a camera-flash application, if the camera/cell-phone/tablet/etc. produces pictures with non-uniform illumination, the purchaser of the camera/cell-phone/tablet/etc. will likely demand a replacement. 
         [0008]    Although fairly simple techniques are available to properly align the substrate with the tool that provides the molded lens structure, such as creating alignment features in each of the substrate and the tool, achieving a correspondingly proper alignment of the light emitting element on the substrate is a more challenging and costly task, requiring, for example, a high-precision ‘pick-and-place’ machine to place each light emitting element at a highly-precise location on the substrate. 
         [0009]    In order to avoid the aforementioned double-handling of the light emitting element, technologies have evolved to provide light emitting dies that are self-supporting, and can be handled directly. WO 2013/084155, “FORMING THICK METAL LAYERS ON A SEMICONDUCTOR LIGHT EMITTING DEVICE”, published 13 Jun. 2013 for Schiaffion, Akram, Basin, Munkhol, Lei, and Nickel, and incorporated by reference herein, discloses light emitting elements that have thick metal layers that provide the structural support required for routine handling of the elements, eliminating the need for a supporting substrate. Because the self-supporting chip can be handled without further packaging, it is commonly termed a “Chip Scale Package” (CSP). 
         [0010]    However, even though these self-supporting chips do not require a structural substrate, the conventional encapsulation processes still require that these chips be placed on some form of substrate, to allow multiple chips to be encapsulated at the same time, with the accompanying difficulty in assuring alignment of the light emitting chip and the attached lens structure. 
       SUMMARY OF THE INVENTION 
       [0011]    It would be advantageous to provide a method and system that facilitates accurate alignment of light emitting chips and their associated lens structures. It would also be advantageous if this method and system are suitable for mass production processes. To better address one or more of these concerns, in an embodiment of this invention, a lens structure is pre-formed with features that facilitate accurate alignment of a light emitting chip within the lens structure. To ease manufacturing, the features include tapered walls that allow for easy insertion of the light emitting chip into the lens structure, the taper serving to accurately align the light emitting chip when the chip is fully inserted. The taper may include linearly sloped or curved walls, including complex shapes. An adhesive may be used to secure the light emitting chip to the lens structure. The light emitting chips may be ‘picked and placed’ into an array of lens structures, or ‘picked and placed’ onto a substrate that may be overlayed by the array of lens structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: 
           [0013]      FIGS. 1A-1B  illustrate an example profile and bottom view of a lens structure with sloped walls and channels that facilitate the exit of air bubbles and adhesives.  FIG. 2  illustrates an example profile view of a lens structure with stepped and sloped walls. 
           [0014]      FIGS. 3A and 3B  illustrate example sheets of lens structures with tapered cavities. 
           [0015]      FIGS. 4A-4D  illustrate example profiles of complex tapered cavities. 
           [0016]      FIG. 5  illustrates an example bottom view of a lens structure with a conic-section cavity. 
           [0017]      FIGS. 6A and 6B  illustrate alternative optical elements. 
       
    
    
       [0018]    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 
       [0019]    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. 
         [0020]      FIGS. 1A-1B  illustrate an example profile and bottom view of a lens  100  that includes a cavity  150  for receiving a light emitting device (LED)  110 , and an optical element  140  that provides a desired light output pattern when light is emitted from the LED  110 . In this example, the optical element  140  is a hemispherical dome that provides a substantially uniform light output pattern across its field of view. 
         [0021]    The lens  100  may comprise silicone, a silicone epoxy hybrid, glass, or any transparent optical material with an appropriate refractive index. The LED  110  may be a self-supporting device, such as a chip-scale-package (CSP), or a thin film die mounted on a ceramic substrate (die on ceramic, DOC), with contacts  120  on the surface opposite the light emitting surface  130 . Other LED structures may also be used. 
         [0022]    As illustrated, to ease assembly, the cavity  150  is tapered, and includes sloped walls  160 . The bottom surface  170  of the cavity  150  is dimensioned so as to situate the light emitting device  110  at a fixed location within the cavity  150  within a given precision, based on the requirements of the intended application. In this example, the bottom surface  170  has substantially the same dimensions as the light emitting device, although it may be slightly larger, depending upon the tolerances of the light emitting device. The required precision of the location of the light emitting device  110  with respect to the lens structure  100  may dictate the allowable over-sizing, if any, of the bottom surface  170 . 
         [0023]    An adhesive having a refractive index that is equal to the refractive index of the LED  110  or the lens  100 , or a value between the refractive indexes of the LED  110  and lens  100  may be dispensed into the cavity  150  before the LED  110  is inserted into the cavity. Depending upon the particular assembly technique, the adhesive may also, or alternatively, be dispensed upon the LED  110  prior to insertion into the cavity  150 . 
         [0024]    As illustrated in  FIGS. 1A and 1B , channels  180  may be provided to enable air and excess adhesive to escape during the assembly process. These channels  180  are illustrated as cylindrical borings in  FIGS. 1A and 1B , although other shapes may be used; for example, if the cavity is formed by a molding process, the channels may have the same slope as the sloped walls  160 . 
         [0025]    The channels  180  are illustrated at each corner of the cavity  150 , although other locations, and fewer or more channels may be provided. In one alternative channels located at the sides of the LED  100  and away from the corners may be used to avoid rotational alignment errors. The size, shape, and location of the channels may be altered depending upon multiple factors including, for example, the viscosity of the adhesive, and the overall size of the LED  110 . 
         [0026]    In another embodiment, the LED  110  is inserted into the cavity without an adhesive between the light emitting surface  130  and the bottom surface  170  of the cavity  150 . A thin film of index-matched liquid may be used to provide an efficient optical coupling between the LED  110  and the bottom surface  170 . After insertion, an adhesive may be administered in the space between the LED  110  and the sloped walls  160 . This post-insertion application of the adhesive may eliminate or minimize the need for the channels  180 . 
         [0027]    To ease subsequent mounting of the lens  100  with LED  110  on a subsequent substrate, such as a printed circuit board, the depth of the cavity  150  may be determined such that the contacts  120  extend slightly above (‘proud of’) the underside  101  of the lens  100  when the light emitting device is fully situated within the cavity. A depth that is about 50-500 μm less than the total height of the LED  110 , including contacts  120 , generally provides a sufficient pride 0  of the contacts beyond the underside  101  of the lens  100 , although other depths may be used, depending upon the tolerance requirements of the application. For example, if the LED  110  is a self-supporting chip-scale package, with fine tolerances, a nominal proud as small as Sum may be used. 
         [0028]    By shaping the taper such that the opening of the cavity  150  is larger than the dimensions of the LED  110 , insertion of the LED  110  into the cavity  150  is simplified. 
         [0029]    By shaping the taper such that the cross-section of the cavity  150  narrows in a direction toward the bottom surface  170 , variance in the location of the LED  110  within the lens  100  is substantially controlled, providing for a self-alignment of the LED  110  as it is inserted into the lens  100 . This taper also provides this self-alignment independent of the means used to insert the LED  110  into the cavity  150 . Even a manual insertion of the LED  110  into the cavity  150  will provide the same accuracy and precision as an automated insertion using a highly accurate and precise pick-and-place machine. In like manner, a pick-and-place machine of minimal accuracy and precision may be used while still maintaining the same high level accuracy and precision. 
         [0030]    As illustrated in  FIG. 2 , the profile of the cavity  250  of lens  200  may be adjusted to conform to the shape of the light emitting device  210 . In this example, the light emitting device  210  includes a wavelength conversion layer  230 , such as a phosphor-embedded silicone that is molded upon the light emitting device  210 . A recess  265  at the entry to the cavity  250  is shaped to accommodate the lip  235  formed by this example wavelength conversion layer  230 . 
         [0031]    Below the recess  265 , the cavity  250  includes sloped walls  260  to facilitate insertion of the light emitting device  210 , and a bottom surface  270  that serves to locate the light emitting device within the lens  200  within a given precision, as detailed above with regard to surface  170  of lens  100 . 
         [0032]      FIGS. 3A and 3B  illustrate example sheets  300 ,  300 ′ of lenses  100 ,  100 ′ with cavities  150 . Although only a few lenses  100 ,  100 ′ are illustrated, one of skill in the art will recognize that the sheets  300 ,  300 ′ may include hundreds of lenses  100 ,  100 ′. For ease of illustration, the venting channels  180  of each cavity  150  of  FIGS. 1A-1B  are not illustrated, but may be present. 
         [0033]    In the example of  FIG. 3A , sheet  300  includes sixteen lenses  100 , each with a single cavity  150 . This sheet may comprise, for example silicone, a silicone epoxy hybrid, glass, or any other transparent optical material that can be formed with defined cavities. 
         [0034]    In an example manufacturing process, a pick and place machine may be used to insert each LED  110  (not illustrated) into each cavity  150 . The pick and place machine may be configured to place each LED  110  at the center of each cavity  150 , but with sufficient compliance during the insertion to enable the LED  110  to be guided by the walls of the cavity  150  into the desired location. Alternatively, the pick and place machine may place each LED  110  partially into each cavity  150 , and a subsequent process, such as a plate press may be used to complete the insertion of the LEDs  110  into the cavities  150 . 
         [0035]    In an alternative process, the LEDs are arranged on a temporary substrate, such as a conventional “dicing tape”, at appropriate locations, and the sheet  300  is mated with these LEDs on the substrate, by either overlaying the sheet  300  upon the LEDs, or overlaying the dicing tape with attached LEDs over the sheet  300 . 
         [0036]    In an example embodiment, the sheet  300  is a partially cured silicone that is cured after the LED  110  is inserted into each cavity  150 . The subsequent curing may serve to adhere each LED  110  to each lens  100 , thereby avoiding the need to include an adhesive bond. 
         [0037]    In an alternative embodiment, the sheet  300  is fully formed, and an adhesive may be applied to each cavity  150 , or to each LED  110 , to secure each LED  110  to each lens  100 . In some embodiments, the adhesive is applied after the LEDs  110  are inserted into the cavities  150 , adhering the edges of the LEDs  110  to the walls of the cavities  150 . 
         [0038]    In other embodiments, detailed below, the sheet  300  may comprise a material with some resilience, and the insertion of the LED  110  into the cavity  150  may provide a sufficient friction force to maintain the LED  110  at the appropriate location within the lens  100 . 
         [0039]    A material that facilitates optical coupling between the light emitting surfaces of the LEDs  110  and the lenses  100  of the sheet  300  may be applied to either the cavities  150  or the LEDs  110 . 
         [0040]    In like manner, a material that serves to reflect light that strikes the edges of the LED  110  may be applied to the edges of the LED  110 , for example, by filling the gap between the LED  110  and the sloped walls of the cavity  150  with such material. 
         [0041]    Upon completion of the insertion and adhering of the LEDs  110  in the cavities  150  of the lenses  100 , the sheet  300  may be sliced/diced along the cutting lines  320 - 370  to provide singulated LED with lens assemblies. In some embodiments multiple LED with lenses may be provided as a single assembly, for example, by only slicing along lines  330  and  360 , providing four assemblies, each assembling including four LEDs with individual lenses. 
         [0042]    One of skill in the art will recognize that the example one-to-one relationship between LEDs and lenses of the previous figures is merely one of many configurations. For example,  FIG. 3B  illustrates an embodiment wherein multiple LEDs are intended to be inserted into multiple cavities  150  of each lens  100 ′. In such an embodiment, the cavities  150  of each lens  100 ′ may be more closely situated than the cavities  150  of each lens  100  of  FIG. 3A . 
         [0043]    In some embodiments, one or more of the cavities  150  may be configured to accommodate multiple LED dies, which may be arranged on a single substrate. In other embodiments, the cavities  150  within each lens  100 ′ may be of different sizes, to accommodate a mix of different LED types within the lens  100 ′, such as a combination of different color LEDs. 
         [0044]    As in the example of  FIG. 3A , the LEDs  110  (not illustrated) may be inserted into each cavity manually, or via a pick-and-place process. Or, the LEDs  110  may be arranged on a temporary substrate at locations corresponding to cavities  150  on the sheet  300 ′, and subsequently mating the sheet  300 ′ and the substrate containing the LEDs  110 . Similarly, the LEDs  110  may be adhered to the lenses  100 ′ using any of the above described techniques, or any other viable and reliable technique. 
         [0045]    Upon completion of the insertion and adhering of the LEDs  110  into the cavities  150  of each lens  100 ′, the lenses  100 ′ may be singulated by slicing/dicing the sheet  300 ′ along the cutting lines  380 ,  390 . 
         [0046]    One of skill in the art will recognize, in view of this disclosure, that this invention is not limited to the example use of cavities  150  with linearly sloped walls  160 . 
         [0047]      FIGS. 4A-4D  illustrate alternative cavity profiles. As in  FIGS. 3A-3B , the venting channels  180  of  FIG. 1  are not illustrated in these figures, for ease of illustration, but may be included in each example embodiment. 
         [0048]      FIG. 4A  illustrates a profile comprising wall segments  410 ,  420  having different slopes. The upper wall segment  410  has a relatively shallow slope to provide a wide opening for inserting the LED (not illustrated), while the wall segment  420  has a relatively steep slope, and may be orthogonal to the surface  470 , to provide a larger surface area for constricting the edges of the LED to maintain the proper location of the LED within the cavity. 
         [0049]    Depending upon the material in which the cavity is formed, the closeness of the fit between the size of the LED and the size of the surface  470 , the slope of the lower wall segment  420 , and the size of the venting channels  180  (not illustrated), this embodiment may require substantial force to insert each LED into each cavity.  FIGS. 4B-4D  illustrate alternative profiles that may require less insertion force. 
         [0050]    In  FIG. 4B , the upper wall segment  430  is sloped to provide an opening that is larger than the size of the intended LED, and the lower wall segment  420  is sloped in an opposite direction to create protrusions  435  that serve to constrict the edges of the LED to maintain the proper location of the LED within the cavity. However, as compared to  FIG. 4A , the edges of the LED will only contact these protrusions  435 , and not the entire surface of the lower wall segment  440 . The reversed slope of the wall segment  440  provides a lower surface  470  that is wider than the LED that is containing between the protrusions  435 , providing some room for the displaced air or adhesive, reducing or eliminating the reliance on the venting channels  180 . 
         [0051]    In  FIG. 4C , a curved wall segment  450  is used to gradually reduce the cross section area in the direction of the surface  470  in a non-linear fashion, so that the lower portion of the wall segment  450  may be more constraining of the LED compared to the linearly sloped walls  160  of  FIG. 1 , but less constraining compared to the linear wall segment  420  of  FIG. 4A , particularly if the segment  420  is orthogonal to the surface  470 . The continuous curvature of the wall segment  450  may also ease the insertion of the LED, compared to the abrupt edges at the transition between wall segment  410  and  420  of  FIG. 4A . 
         [0052]      FIG. 4D  illustrates a combination of curved  460  and linear  490  wall segments, as well as the addition of features  480  that may secure the LED while introducing minimal insertion resistance. The features  480  may be a continuous ridge within the cavity, or a plurality of individual bead-like protrusions from the wall segment  490 . If individual protrusions are used, the insertion resistance is reduced, and the space between the protrusions allows for the displaced air and adhesive to escape, potentially avoiding the need for the venting channels  180  of  FIG. 1 . One of skill in the art will recognize, in light of this disclosure, that any of a variety of other profiles may be used to fix the location of the LED within the lens within a given tolerance, while also allowing for practical insertion forces. 
         [0053]    One of skill in the art may also recognize that the shape of the cavity, or the shape of the surface of the cavity, need not match the shape of the LED. Depending upon the processes and materials used to create the lens, creating a rectangular cavity, such as illustrated in  FIG. 1B , may not be economically viable. If, for example, the lens is a rigid material, boring or grinding a circular cavity may be substantially less expensive than creating a rectangular cavity. 
         [0054]      FIG. 5  illustrates an example lens  500  that includes a conical cavity  550  with a sloped wall  560  that forms a circular bottom surface  570 . The diameter of the surface  570  is such that it circumscribes the LED  110 , providing contact points  590  on the wall of the cavity that center the LED  110  at the center of the surface  570 . The semicircular gaps  575  around LED  110  allows for the displaced air and adhesive to escape, potentially avoiding the need for the venting channels  180  of  FIG. 1   
         [0055]    As contrast to the rectangular surface  170  of  FIG. 1B , the conic cavity  550  and circular surface  570  may allow the LED  110  to rotate during the insertion process, but if the optical properties of the lens  500  are symmetric about the center axis, the rotation of the LED  110  about this center axis will have no effect on the accuracy and precision of locating the LED  110  at that center axis. If the lens  500  is a partially cured silicone, the compliance of the partially cured silicone may enable the LED  100  to “dig in” to the silicone at the corners  590 , thereby controlling or limiting the rotation. 
         [0056]    It is significant to note that all of the above example profile views could also be profile views of half-sections of conic cavities, although the profiles of  FIGS. 4B and 4D  would more likely be formed by a molding process, rather than a boring or grinding process, and achieving a rectangular cavity via a molding process is relatively straightforward. 
         [0057]    One of skill in the art will also recognize that the optical element of the lens is not limited to the hemispherical dome  140  of  FIGS. 1A-1B .  FIGS. 6A and 6B  illustrate an example side emitting optical element  600 , and an example collimating optical element  650 , respectively. Other optical elements may be used to achieve desired light output patterns. 
         [0058]    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. 
         [0059]    For example, it is possible to operate the invention in an embodiment wherein additional elements may be included within the cavity. For example, a wavelength conversion material may be inserted into the cavity before the light emitting device is inserted. Alternatively, or additionally, the lens may include a wavelength conversion material, or the light emitting device may include a wavelength conversion material. In some embodiments, the wavelength conversion material may serve as an adhesive layer between the light emitting device and the lens. 
         [0060]    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.