Patent Publication Number: US-2011062470-A1

Title: Reduced angular emission cone illumination leds

Description:
FIELD OF INVENTION 
     The present disclosure relates to light emitting diode (LED) packages and, in particular, to LED packages that meets glare regulations for overhead lighting. 
     DESCRIPTION OF RELATED ART 
     Overhead lighting fixtures may have to meet glare regulations that limit brightness over certain emission angle (e.g., less than 1000 cd/m 2  for angles greater than 65 degrees). Some lighting fixtures use diffusers to limit their emission angles. These diffusers may impact the aesthetics of the lighting fixtures by increasing the thickness of the lighting fixtures. 
     More and more lighting fixtures are using light emitting diodes (LEDs) are their light source because LEDs are energy efficient and have a long life. LEDs typically generate Lambertian emissions that do not meet the glare regulations for overhead lighting. Thus, what are needed are LEDs that generate radiation patterns that meet glare regulations for overhead lighting. 
     SUMMARY 
     In one or more embodiments of the present disclosure, a light emitting diode (LED) package includes an integrated package level reflector formed around an LED die. The reflector reduces the light emission angle of the LED package so the LED package may be used as a light source in overhead light fixtures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  illustrates a cross-sectional view of an LED package with a lens integrated with a package level reflector; 
         FIG. 2A  illustrates a cross-sectional view of the lens of  FIG. 1 ; 
         FIG. 2B  illustrates an enlarged portion of  FIG. 2A  showing an encapsulation/bonding material between a wavelength converting element and the lens; 
         FIG. 3  is a flowchart of a method for fabricating the LED package of  FIG. 1 ; 
         FIG. 4  illustrates a cross-sectional view of an LED package with a package level reflector molded on a support for the LED die; 
         FIG. 5  is a flowchart of a method for fabricating the LED package of  FIG. 4 ; 
         FIG. 6  illustrates a cross-sectional view of an LED package with a support integrated with a package level reflector; and 
         FIG. 7  is a flowchart of a method for fabricating the LED package of  FIG. 6 , all arranged in accordance with embodiments of the present disclosure. 
     
    
    
     Use of the same reference numbers in different figures indicates similar or identical elements. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a cross-sectional view of a light emitting diode (LED) package  100  with a lens  102  integrated with an integrated package level reflector  104  in one or more embodiments of the present disclosure. Lens  102  encapsulates an LED die  106  on a support  108 . Support  108  may include a submount or interposer  110 , a heat sink  112 , and a leadframe or housing  114 . LED die  106  is mounted on interposer  110 . Interposer  110  has conductive traces that electrically couple LED die  106  to bond wire pads on the interposer. Interposer  110  is mounted on heat sink  112 . Heat sink  112  dissipates heat from LED die  106 . Heat sink  112  is received in housing  114 . Bond wires (not shown) electrically couple the pads on interposer  110  to electrical leads  116  of housing  110 , which pass electrical signals between LED package  100  and external components. 
     LED die  106  may include an n-type layer, a light-emitting layer (common referred to as the “active region”) over the n-type layer, a p-type layer over the light-emitting layer, a conductive reflective layer over the p-type layer, and a guard metal layer over the conductive reflective layer. One or more n-type bond pads provide electrically contact to the n-type layer, and one or more p-type bond pads provide electrical contact to the conductive reflective layer for the p-type layer. The lateral sides of LED die  106  are covered by a reflective or scattering coating  118  to limit edge emission. Coating  118  may be a polymer or a resin with reflective particles, such as silicone, epoxy, or acrylic with TiO 2 . Coating  118  may also be a thin metal film such as Al, Ag, Cr, Au, Ni, V, Pt, Pd, or a combination thereof. 
     A wavelength converting element  120  may be located over LED die  106  to modify the emission spectrum and provide a desired color light. Wavelength converting element  120  may be one or more phosphor layers applied to the top of LED die  106 , or one or more ceramic phosphor plates bonded to the top of the LED die. Ceramic phosphor plates are described in detail in U.S. Pat. No. 7,361,938, which is commonly assigned and incorporated herein by reference. An encapsulation/bonding material may be placed between lens  102  and wavelength converting element  120 . The encapsulation/bonding material may be a silicone having a refractive index of 1.33 to 1.53. 
     Instead of being bonded to LED die  106 , the ceramic phosphor plates may be bonded to lens  102  as described in U.S. patent application Ser. No. ______ entitled “Molded Lens Incorporating a Window Element,” attorney docket no. PH012893US1, which is concurrently filed, commonly assigned, and incorporated herein by reference. The lateral sides of wavelength converting element  120  are covered by a reflective or scattering coating  119  to limit edge emission. Coating  119  may be the same material as coating  118 , and they may be applied at the same time. An encapsulation/bonding material may be placed between wavelength converting element  120  and LED die  106  when lens  102  is mounted on support  108 . The encapsulation/bonding material may be a silicone having a refractive index of 1.33 to 1.53. 
       FIG. 2A  illustrates a cross-sectional view of lens  102  in one or more embodiments of the present disclosure. Lens  102  is solid and has a dome shape that improves light extraction. Lens  102  has a flange  202  around the perimeter of its bottom surface that fits into a groove in housing  114 . Lens  102  may be a material with a refractive index similar to the underlying element to improve light extraction. Lens  102  may be glass with a refractive index of 1.5 to 1.8. 
     Reflector  104  is one or more cavities formed in the bottom surface of lens  102 . Reflector  104  is filled with air or a material having a lower refractive index than lens  102 . One or more reflective surfaces  204  are created at the medium boundary between lens  102  and reflector  104  from total internal reflection (TIR). The lower index material may be a silicone with a refractive index of 1.33 to 1.53. The silicone may also serve as an adhesive and an encapsulation material between lens  102  and support  108 . Instead of utilizing coatings  118  and  119  to limit edge emission from LED die  106  and wavelength converting element  120 , the lower index material may include reflective particles to serve the same function. The reflective particles may be TiO 2 . 
     Reflective surfaces  204  reflects light emitted from LED die  106  or wavelength converting element  120  to limit the emission angle of LED package  100 , as demonstrated by light rays  206  and  208 . The shapes of reflective surfaces  204  depend on the desired emission angle of LED package  100 . Reflective surfaces  204  may be flat or curved, and they may be asymmetrical (as demonstrated by reflective surface  204  and phantom reflective surface  204 A). 
       FIG. 2B  shows that encapsulation/bonding material  122  may refract a light ray  210  as it travels from encapsulation/bonding material  122  to lens  102 . The refractive index of encapsulation/bonding material  122  may be less than the refractive index of lens  102 . The shape of reflective surfaces  204  may need to consider any refraction of the light at the interface between encapsulation/bonding material  122  and lens  102  in order to produce the desired emission angle of LED package  100 . 
     Referring back to  FIG. 2A , reflector  104  has the same layout as LED die  106  or wavelength converting element  120  so the reflector is located immediately adjacent to the final light emitting surface once lens  102  is mounted on support  108 . For example, reflector  104  may have a triangular cross-section with flat reflective surfaces  204 . The shape of reflector  104  and reflective surfaces  204  may be determined using an optical design software, such as LightTools from Optical Research Associates of Pasadena, Calif. 
       FIG. 3  is a flowchart of a method  300  for fabricating LED package  100  in one or more embodiments of the present disclosure. In process  302 , lens  102  is molded with reflector  104 . Process  302  is followed by process  304 . 
     In process  304 , reflector  104  is optionally filled with a material having a lower refractive index than lens  102 . Alternatively reflector  104  is left empty so it is filled with air after lens  102  is mounted on support  108 . Process  304  is followed by process  306 . 
     In process  306 , support  108  is assembled from interposer  110 , heat sink  112 , and housing  114 , and LED die  106  is mounted on the interposer of the support. Wavelength converting element  120  may be formed on or bonded to the top of LED die  106  before the LED is mounted on support  108 . The lateral sides of LED die  106  and the wavelength converting element  120  are then covered by reflective or scattering coatings  118  and  119 . Process  306  is followed by process  308 . 
     In process  308 , lens  102  is mounted on support  108  to encapsulate LED die  106  and wavelength converting element  120  to complete LED package  100 . Flange  202  of lens  102  is fit into a groove in housing  114  and an outer portion of the groove is plastically deformed over the flange to secure and seal the lens to the housing. As described above, an encapsulation/bonding material may be placed between lens  102  and wavelength converting element  120 . 
     In method  300 , reflector  104  may be filled with the lower index material after lens  102  is mounted to support  108  through conduits in housing  114 . In method  300 , wavelength converting element  120  may also be bonded to lens  102  instead of LED die  106 . As described above, an encapsulation/bonding material may be placed between wavelength converting element  120  and LED die  106 . 
       FIG. 4  illustrates a cross-sectional view of an LED package  400  with a package level reflector  404  molded on a support  408  for an LED die  406  in one or more embodiments of the present disclosure. Although not shown, support  408  may include an interposer, a heat sink, and a housing as described above for support  108 . LED die  406  may be similarly constructed as LED die  106 . 
     A wavelength converting element  420  may be located over LED die  406  to modify the emission spectrum and provide a desired color light. Wavelength converting element  420  may be one or more phosphor layers applied to the top of LED die  406 , or one or more ceramic phosphor plates bonded to the top of the LED die. Ceramic phosphor plates are described in detail in U.S. Pat. No. 7,361,938, which is commonly assigned and incorporated herein by reference. 
     A silicone lens  402  is molded over support  408  to encapsulate LED die  406  and reflector  404 . Reflector  404  may be a low index silicone having a refractive index of 1.33 to 1.53, and lens  402  may be a high index silicone having a refractive index of 1.41 to 1.7. The silicone of reflector  404  may include reflective particles to add a scattering property to the reflector. The reflective particles may be TiO 2 . The scattering property of reflector  404  is used to limit edge emission from LED die  406  and wavelength converting element  420 . 
     One or more angled reflective surfaces  422  are created at the medium boundary between lens  402  and reflector  404  from total internal reflection. Reflective surfaces  422  reflect light emitted from LED die  406  or wavelength converting element  420  to limit the emission angle of LED package  400 , as demonstrated by light rays  426  and  428 . The shape of reflective surfaces  422  depends on the desired emission angle of LED package  400 . Reflective surfaces  422  may be flat or curved, and they may be asymmetrical (as demonstrated by reflective surface  422  and phantom reflective surface  422 A). Reflector  404  generally follows the perimeter of LED die  406  or wavelength converting element  420  so the reflector is located immediately adjacent to the final light emitting surface. The shape of reflector  404  and reflective surfaces  422  may be determined using an optical design software, such as LightTools from Optical Research Associates of Pasadena, Calif. 
       FIG. 5  is a flowchart of a method  500  for fabricating LED package  400  in one or more embodiments of the present disclosure. In process  502 , support  408  is assembled from its components, if any, and LED  406  is mounted on the support. Wavelength converting element  420  may be formed on or bonded to the top of LED  406  before the LED is mounted on support  408 . Process  502  is followed by process  504 . 
     In process  504 , the reflector material is applied over support  408  around LED die  406  and wavelength converting element  420 . Process  504  is followed by process  506 . 
     In process  506 , the reflector material is molded to form reflector  404 . A mold may be pressed onto the reflector material to form reflector  404 . Process  506  is followed by process  508 . 
     In process  508 , lens  402  is molded over support  408  to encapsulate LED  406 , wavelength converting element  420 , and reflector  402  to complete LED package  400 . 
       FIG. 6  illustrates a cross-sectional view of an LED package  600  with a support  608  integrated with a package level reflector  604  in one or more embodiments of the present disclosure. Support  608  may be a leadframe or an interposer such as a metal core printed circuit board (MCPCB). An LED die  606  is mounted on support  608 . LED die  606  may be similarly constructed as LED die  106 . 
     A wavelength converting element  620  may be located over LED die  606  to modify the emission spectrum and provide a desired color light. Wavelength converting element  620  may be one or more phosphor layers applied to the top of LED die  606 , or one or more ceramic phosphor plates bonded to the top of the LED die. Ceramic phosphor plates are described in detail in U.S. Pat. No. 7,361,938, which is commonly assigned and incorporated herein by reference. 
     The lateral sides of LED die  606  and wavelength converting element  620  are covered by a reflective or scattering coating  618  to control edge emission. Coating  618  may be a polymer or a resin with reflective particles, such as silicone, epoxy, or acrylic with TiO 2 . Coating  618  may also be a thin metal film such as Al, Ag, Cr, Au, Ni, V, Pt, Pd, or a combination thereof. A silicone lens  602  is molded over support  608  to encapsulate LED die  606  and wavelength converting element  620 . 
     Reflector  604  has one or more angled reflective surfaces  622  covered with a reflective coating  624 . Reflective coating  624  may be a thin metal film such as Al, Ag, Cr, Au, Ni, V, Pt, Pd, or a combination thereof. Reflective coating  624  may be the same material coating  618 , and they may be applied at the same time. 
     Reflective surfaces  622  reflects light emitted from LED die  606  or wavelength converting element  620  to limit the emission angle of LED package  600 , as demonstrated by light rays  626  and  628 . The shape of reflective surfaces  622  depends on the desired emission angle of LED package  600 . Reflective surfaces  622  may be flat or curved, and they may be asymmetrical (as demonstrated by reflective surface  622  and phantom reflective surface  622 A). Reflector  604  defines a cup for receiving LED die  606  and wavelength converting element  620 . The shape of reflector  604  and reflective surfaces  622  may be determined using an optical design software, such as LightTools from Optical Research Associates of Pasadena, Calif. 
       FIG. 7  is a flowchart of a method for fabricating the LED package  600  in one or more embodiments of the present disclosure. In process  702 , support  608  is fabricated with reflector  604  having angled reflective surface  622  and a cup for receiving LED die  606 . Process  702  is followed by process  704 . 
     In process  704 , LED  606  is mounted to support  608  in the cup defined by reflector  604 . Wavelength converting element  620  may be formed on or bonded to the top of LED  606  before the LED is mounted on support  608 . Process  704  is followed by process  706 . 
     In process  706 , coating  618  is applied to the lateral sides of LED die  606  and wavelength converting element  620 , and coating  624  is applied over reflective surface  622 . Process  706  is followed by process  708 . 
     In process  708 , lens  602  is molded over support  608  to encapsulate LED  606  and wavelength converting element  620  to complete LED package  600 . 
     Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. Numerous embodiments are encompassed by the following claims.