Patent Publication Number: US-2007102718-A1

Title: Lens in light emitting device

Description:
BACKGROUND  
      Referring to  FIGS. 16-18 , there is shown a side emitting light emitting diode (LED) package  5  for providing light to a light guide  10  ( FIG. 18 ). Light guide  10  is typically used for backlighting of a liquid crystal display (LCD) (not shown) with LED package  5  as the light source for light guide  10 .  
      Referring to  FIG. 17 , there is shown a cross-sectional view of LED package  5 . Light emitting diode (LED) dice  15  are in attachment to the bottom of a substrate  20 , and within walls  25  forming an elongate cavity  30 . Generally, a transparent encapsulation material  35  is disposed inside of elongate cavity  30  to cover the LED dice  15 . Transparent encapsulation material  35  may fill elongate cavity  30  to an aperture  40  formed by walls  25 .  
      Typically, there are provided wire connects between an electrode on each one of LED dice  15  and bonding pads on substrate  20 . On an outer surface of walls  25 , electrodes may be electrically connected to a motherboard, and the pathway from the motherboard through the electrodes supplies electrical current to the LED dice  15 . The number of LED dice  15  depends on the design of substrate  20  and light guide  10 .  
      For side-emitting LED dice  15  used as a light source for light guide  10 , LED package  5  is normally located very close to light guide  10  in order to avoid light loss between LED package  5  and light guide  10 .  
      Normally, side emitting LED package  5  is designed to deliver as much light as possible to light guide  10 . A convex lens may be mounted on the outer surface of the encapsulate material, and outside of aperture  40 , to collimate light into a direction toward light guide  10 . However, the configuration with the convex lens mounted on the outer surface of the encapsulate material is generally not recommended because some light goes through a side area of the convex lens and never goes into light guide  10 .  
      Typically, LED package  5  contains red, green and blue (RGB) LED dice  15  in elongate cavity  30 . Using RGB LED dice  15  as the light source for the backlight of light guide  10  into the LCD generally provides a wide color range, but requires an area for color mixing. If color mixing is accomplished inside of LED package  5 , which generates mostly white light, light guide  10  will generally require a smaller area for color mixing. Controlling light from LED dice  15  in elongate cavity  30  is limited without the use of a convex lens outside of aperture  40 , on encapsulation material  35 .  
      A reflector cup within elongate cavity  30  may be provided in order to provide good color mixing without the use of a lens. The reflector cup acts to control the direction of light from one or more of LED dice  15 . However, the reflector cup only controls the direction of light from the side of a die and does not control the direction of reflected light traveling in a direction from the top of the die through aperture  40 .  
      Referring now to  FIGS. 19 and 20 , for a single die of LED dice  15  in LED package  5 , there is shown a radiation pattern plot  45  for the LED ( FIG. 19 ) and a schematic diagram of a ray trace simulation  50  in the vertical direction away from the die ( FIG. 20 ). For radiation pattern plot  45  and ray trace simulation  50 , side emitting LED package  5  is filled with transparent encapsulation material  35  and no lens is disposed in the light path. Transparent encapsulation material  50  fills the whole elongate cavity  30  of substrate  20  as shown in  FIG. 17 , only one die of dice  15  is activated, and the radiation pattern of plot  45  is measured at a location outside of LED package  5 . On the vertical direction, viewing angle tends to be wide and radiation pattern has several peaks. This is due to the refraction of the light from the die at the flat surface of transparent encapsulation material  35 , and the light is bent toward a far angle. Also, the reflected light that is reflected at the wall of housing goes to a direction with a larger angle from the 0 degree, on-axis direction.  
     SUMMARY OF THE INVENTION  
      In an embodiment, there is provided an opto-electronic package comprising a substrate having a base and a plurality of cavity-defining walls, the base and the plurality of cavity-defining walls defining an elongate cavity having a major axis, a minor axis and an aperture, and the base having a surface that presents within the cavity; a plurality of light emitting diode (LED) dice mounted to the surface of the base that presents within the elongate cavity of the substrate so as to project light within the elongate cavity; and at least one lens disposed between the cavity-defining walls and having a maximum height remaining within the aperture of the elongate cavity, and the at least one lens having a convex orientation relative to at least one of the plurality of light emitting diode (LED) dice along the minor axis of the elongate cavity of the substrate.  
      In another embodiment, there is provided a system for backlighting an LCD screen, the system comprising an opto-electronic package, comprising a substrate having a base and a plurality of cavity-defining walls, the base and the plurality of cavity-defining walls defining an elongate cavity having a major axis, a minor axis and an aperture, and the base having a surface that presents within the cavity; a plurality of light emitting diode (LED) dice mounted to the surface of the base that presents within the elongate cavity of the substrate so as to project light within the elongate cavity; and at least one lens disposed between the cavity-defining walls and having a maximum height remaining within the aperture of the elongate cavity, and the at least one lens having a convex orientation relative to at least one of the light emitting diode (LED) dice along the minor axis of the elongate cavity of the substrate; a light guide having an input portion and an output portion, the input portion operatively associated with the aperture to receive light provided by the plurality of light emitting dice (LED) dice, and the output portion operatively associated with the LCD screen to transmit the light from the input portion to the LCD screen.  
      In another embodiment, there is provided a method of manufacturing an opto-electronic package, comprising fabricating a substrate having a base and a plurality of cavity-defining walls, the base and the plurality of cavity-defining walls defining an elongate cavity having a major axis and an aperture, the base having a surface that presents within the cavity; attaching a plurality of light emitting diode (LED) dice to the base of the substrate within the cavity; and disposing at least one lens between the cavity-defining walls and entirely within the aperture of the elongate cavity, and the at least one lens having a convex orientation relative to at least one of the plurality of light emitting diode (LED) dice along the minor axis of the elongate cavity of the substrate.  
      Other embodiments are also disclosed.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Illustrative embodiments of the invention are illustrated in the drawings, in which:  
       FIG. 1  illustrates an embodiment of an LED package for a light source;  
       FIG. 2  illustrates a cross-sectional view of the LED package shown in  FIG. 1 ;  
       FIG. 3  illustrates a radiation pattern plot for an LED package shown in  FIG. 1 ;  
       FIG. 4  illustrates a single lens disposed over a single LED die;  
       FIG. 5  illustrates a ray trace simulation in the horizontal direction for the LED die contained in the LED package shown in  FIG. 1 ;  
       FIG. 6  illustrates a ray trace simulation in the vertical direction for the LED die contained in the LED package shown in  FIG. 1 ;  
       FIG. 7  illustrates an embodiment of an LED package for a light source;  
       FIG. 8  illustrates a radiation pattern plot for an LED package shown in  FIG. 7 ;  
       FIG. 9 a  ray trace simulation in the vertical direction for the LED die contained in the LED package shown in  FIG. 7 ;  
       FIGS. 10-13  illustrate an embodiment of an LED package manufactured with a jig;  
       FIG. 14  illustrates an embodiment of a system having an LED package with a lens disposed within the aperture to direct light into a light guide;  
       FIG. 15  is a flow diagram illustrating an embodiment of a method of manufacturing an LED package;  
       FIGS. 16 and 17  illustrate an LED package;  
       FIG. 18  illustrates a system having an LED package and a light guide;  
       FIG. 19  illustrates a radiation pattern plot for an LED package shown in  FIG. 16 ;  
       FIG. 20  illustrates a ray trace simulation in the vertical direction for the LED die contained in the LED package shown in  FIG. 16 ; and  
       FIGS. 21 and 22  illustrate an embodiment of an LED package for a light source having a dimpled surface.  
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT  
      Looking at  FIGS. 1, 2 , and  7 , and in an embodiment, there is shown an opto-electronic package  100  comprising a substrate  105 , a plurality of light emitting diode (LED) dice  110 , and at least one lens  115  disposed between cavity-defining walls  120  and having a maximum height remaining within an aperture  125  of an elongate cavity  130  of substrate  105 .  
      Referring to  FIG. 15 , and in one embodiment, there is disclosed a system  135  for backlighting an LCD screen. System  135  comprises opto-electronic package  100  and a light guide  140 .  
      Referring now to  FIG. 14 , there is shown a method  145  of manufacturing an opto-electronic package. In an embodiment, the method comprises fabricating  150  a substrate, attaching  155  a plurality of light emitting diode (LED) dice to the base of the substrate within the cavity, and disposing  160  at least one lens between the cavity-defining walls and entirely within the aperture of the elongate cavity.  
      Referring again to  FIGS. 1, 2  and  7 , there is shown opto-electronic package  100  comprising substrate  105  having a base  165  and plurality of cavity-defining walls  120 . Base  165  and plurality of cavity-defining walls  120  define an elongate cavity  170  having a major axis  175 , a minor axis  180  and an aperture  185 . Base  165  has a surface  190  that presents within cavity  170 , and plurality of light emitting diode (LED) dice  110  are mounted to surface  190  of base  165  that presents within elongate cavity  130  of substrate  105  so as to project light within elongate cavity  130 . At least one lens  115  is disposed between cavity-defining walls  120  and has a maximum height remaining within aperture  125  of elongate cavity  130 . At least one lens  115  has a convex orientation relative to at least one of plurality of light emitting diode (LED) dice  110  along minor axis  180  of elongate cavity  130  of substrate  105 .  
      Looking at  FIGS. 1, 2 ,  4 ,  5 ,  7 ,  12  and  13 , and in an embodiment, at least one lens  115  may comprise an encapsulation material  195  disposed over light emitting diode (LED)  110  within elongated cavity  130 . In one embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      Referring to  FIGS. 4 and 7 , and in an embodiment, at least one lens  115  may optionally comprise a plastic lens  200  disposed over light emitting diode (LED)  115  within elongated cavity  130 . In one embodiment, encapsulation material  195  may be disposed over light emitting diode (LED)  110  and within plastic lens  200 . In one embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      Looking at  FIGS. 7 and 13 , and in an embodiment, at least one lens  115  is a single lens  205  disposed over the plurality of light emitting diode (LED) dice  115 . In one embodiment, single lens  205  is mounted to surface  190  of base  165  that presents within elongate cavity  130  of substrate  105 . In one embodiment, single lens  205  may comprise encapsulation material  105  disposed over light emitting diode (LED)  110  within elongated cavity  130 . In an embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      Referring to  FIG. 7 , and in an embodiment, single lens  205  may comprise plastic lens  200  disposed over light emitting diode (LED)  110  within elongated cavity  130 . In one embodiment, encapsulation material may be disposed over light emitting diode (LED)  110  and within plastic lens  200  of single lens  205 . In an embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      Looking again at  FIGS. 7, 12  and  13 , single lens  205  may comprise a substantially uniform cylindrical portion  210  having a substantially uniform height in a direction parallel to the major axis of the substrate.  
      Referring now to  FIG. 1 , and in an embodiment, there is shown at least one lens  115  comprising a plurality of lens portions  215 . Corresponding ones of the plurality of light emitting diode (LED) dice  110  and ones of the plurality of lens portions  215  may be in operational association with one another, respectively. In one embodiment, plurality of lens portions  215  each comprise a first length  220  and a second length  225 , the first length extending parallel to the major axis, the second length extending in a direction parallel to the minor axis, and the first length extending a longer distance than the second length.  
      Referring still to  FIG. 1 , each one of plurality of lens portions  215  are discrete from the other ones of the plurality of lens portions  215 . In an embodiment, plurality of lens portions  215  each comprise encapsulation material  195  disposed over light emitting diode (LED)  110  within elongated cavity  130 . In one embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      In an embodiment, plurality of lens portions  215  each comprise plastic lens  200  disposed over light emitting diode (LED)  110  within elongated cavity  130 . In one embodiment, encapsulation material  195  is disposed over light emitting diode (LED)  110  and within plastic lens  200 . In an embodiment, encapsulation material  195  may comprise epoxy. In another embodiment, encapsulation material  195  may comprise silicone.  
      Referring to  FIG. 13 , and in an embodiment, the maximum height of at least one lens  115  is co-planar with aperture  125  of elongate cavity  130 .  
      Referring to  FIGS. 10-13 , and in one embodiment, there is shown substrate  20  having a first end  230  and a second end  235  in opposition to one another along major axis  175 , and wherein the cavity defining walls  120  define a first hole  240  therethrough at first end  230  and define a second hole  245  therethrough at second end  235 . In an embodiment, substrate  105  comprises a plastic material. In another embodiment, substrate comprises a ceramic material.  
      In an embodiment, a jig  250  is selectively disposed within elongate cavity  130  for casting encapsulation material  195  so as to form one or more of the at least one lens  115 .  
      Referring to  FIG. 15 , and in an embodiment, there is shown system  135  for backlighting an LCD screen. Light guide  140  generally includes an input portion  255  and an output portion  260 . Input portion  255  may be operatively associated with aperture  40  to receive light provided by plurality of light emitting dice (LED) dice  110 . Output portion  260  may be operatively associated with the LCD screen to transmit the light from input portion  255  to the LCD screen.  
      In an embodiment, there is provided a method of manufacturing an opto-electronic package. Generally, the method comprises fabricating a substrate having a base and a plurality of cavity-defining walls, the base and the plurality of cavity-defining walls defining an elongate cavity having a major axis and an aperture, the base having a surface that presents within the cavity. The method comprises attaching a plurality of light emitting diode (LED) dice to the base of the substrate within the cavity. The method comprises disposing at least one lens between the cavity-defining walls and entirely within the aperture of the elongate cavity, and the at least one lens having a convex orientation relative to at least one of the plurality of light emitting diode (LED) dice along the minor axis of the elongate cavity of the substrate.  
      In one embodiment, the method may comprise disposing the at least one lens between the cavity-defining walls and entirely within the aperture comprises disposing an encapsulation material over the plurality of light emitting diode (LED) dice within the elongated cavity, and curing the encapsulation material so as to form the at least one lens with the encapsulation material.  
      In relation to the step of disposing the at least one lens between the cavity-defining walls and entirely within the aperture comprises disposing a plastic lens over the plurality of light emitting diode (LED) dice within the elongated cavity, the method may comprise disposing an encapsulation material within the plastic lens and over the plurality of light emitting diode (LED) dice, and curing the encapsulation material so as to form the at least one lens with the plastic lens and the encapsulation material.  
      In relation to the step of disposing a jig through the aperture into the elongated cavity and over the plurality of light emitting diode (LED) dice, the method may comprise disposing an encapsulation material within the jig and over the plurality of light emitting diode (LED) dice, curing the encapsulation material so as to form the at least one lens with the encapsulation material, and removing the jig from the elongated cavity through the aperture.  
      The method may further comprise positioning the substrate to align the major axis in a vertical direction, and disposing the encapsulation material through a first hole defined in the first end into the elongated cavity within the jig and over the plurality of light emitting diode (LED) dice.  
      In one embodiment, lens  115  is created inside of elongate cavity  130 , and the top of lens  115  does not extend from package  100 . One convex lens  205  is applied to one die  110 , and a curvature of lens  205  may be designed for each differing type of die  110 .  
      For the horizontal direction parallel to major axis  175 , light from LED die  110  spreads out and mixes with light from an adjacent die  115  in order to improve color mixing. For the vertical direction parallel to minor axis  180 , light from LED die  110  focuses toward the central axis of light guide  140  for an increase in luminous intensity. In order to optimize color mixing and intensity, curvature for in the horizontal direction and in the vertical direction may be different from one another. A suitably sized aspherical oval lens may be used.  
      Referring to  FIGS. 3, 5  and  6 , for a single die of LED dice  110  in LED package  100  having an aspherical oval lens  115  as shown in  FIG. 1 , there is shown a radiation pattern plot  265  ( FIG. 3 ) for the die, a schematic diagram of a ray trace simulation  270  ( FIG. 5 ) in the horizontal direction and a schematic diagram of a ray trace simulation  275  ( FIG. 6 ) in the vertical direction. The radiation pattern of the die is measured at the same position as the shown in  FIGS. 19 and 20 . The light on horizontal direction is spread out ( FIG. 5 ) by lens  115  to produce a more uniform white color by mixing well with the other light from other ones of dice  110 . In the vertical direction, the light is focused ( FIG. 6 ) by lens  115  to reduce light loss at the coupling to a light guide.  
      Referring now to  FIGS. 8 and 9 , for a single die of LED dice  110  in LED package  5  having a relatively uniform cylindrical portion lens  115  as shown in  FIG. 7 , there is shown a radiation pattern plot  280  ( FIG. 8 ) for the die, a schematic diagram of a ray trace simulation  285  ( FIG. 9 ) in the vertical direction. The radiation pattern of the die is measured at the same position as the shown in  FIGS. 3, 5  and  6  and in  FIGS. 19 and 20 . This cylindrical lens  115  ( FIG. 7 ) may be easier to fabricate than aspherical oval lens  115  while providing enough effect on the vertical direction of emitted light.  
      In order to maximize the effect of lens, the lens may be located at a far distance from the light source LED die, and the size of the lens may be sized relatively large in comparison to the size of the light source. However, the LED die size cannot be sized too small in order to maintain adequate brightness, and the aperture of the housing is normally limited at the width of the light guide for good light coupling. Within these constraints, the top of the lens may be located at the same position as the edge of the housing, and the size of the lens may be sized as large as possible within the aperture size of the substrate.  
      Referring now to  FIGS. 21 and 22 , and in one embodiment, there is shown an opto-electronic package  290  comprising substrate  105  having base  165  and plurality of cavity-defining walls  120 . Base  165  and plurality of cavity-defining walls  120  define an elongate cavity  130  and an aperture  125 . Base  165  has surface  190  that presents within cavity  130 . Plurality of light emitting diode (LED) dice  110  may be mounted to surface  190  of base  165  that presents within elongate cavity  130  of substrate  105  so as to project light within elongate cavity  130 . Encapsulation material  195  is disposed between cavity-defining walls  120  and has a maximum height remaining within aperture  125  of elongate cavity  130 . Encapsulation material has a plurality of dimples  295  formed therein. In an embodiment, dimples  295  formed in an outer surface of encapsulation material  195  may include slight depressions or indentations to form a dimpled surface. In one embodiment, dimples have a radius of about 0.15 mm, a depth of about 0.15 mm, and a pitch of about 0.35 mm. Dimples  295  may be sized and located in encapsulation material  195  to increase the intensity of light through aperture  125 .  
      In an embodiment, the substrate may be made of plastic or ceramics, and some pieces may be built on one sheet of plastic or ceramics in an array. Bond pads and electrodes may be made on the substrate using, for example, plating techniques on plastic or a known via hole techniques on ceramics. After attaching LED dice and connecting the die and wire bond pad with a gold wire, encapsulate material may be disposed into elongate cavity.  
      A jig which has a concave cavity may be used to create the convex lens shape on the encapsulate material during a process of curing the encapsulate material.  
      In an embodiment, the jig is attached on the housing prior to placement of the encapsulate material. The jig is preferably inserted into the elongate cavity and fixed into position along the wall of the substrate. In order to optimize alignment of the lens position to the die position, the jig may be pressed towards the housing during the process of placing and curing the encapsulate material.  
      In order to avoid an air bubble from the encapsulate material, the substrate is preferably held vertically and the encapsulate material is added through a hole located at a bottom position, and air is allowed to escape through another hole at a top position.  
      When the encapsulate material is fully filled, a residual amount of the material may escape the hole at the top position. This residual amount may remain at an outside area of the substrate. This residual amount may be removed by trimming after cure.  
      After curing the encapsulate material, the jig is removed, and each package is separated by sawing or snapping.  
      In an embodiment, convex lenses are fabricated as an array of plastic lenses separate from the package, and these pre-fabricated lenses are each subsequently attached to the substrate of the package. In an embodiment, after die attaching and wire bonding, a liquid type of transparent material is casted in the elongate cavity to cover the LED dice and wires. Before curing the transparent material, the plastic lenses of the array are attached inside of the substrate. The bottom surface of the lens may be either flat or convex shape to prevent an air bubble from being trapped under the bottom surface on top of the transparent material. Each of the lenses in the array may have a hole or a slit to allow escape of the residue of the transparent material. After attaching the lenses of the array, the transparent material may be cured in an oven.