Abstract:
Sideways emission enhancements are described for light emitting diode (LED) lighting solutions having a wide variety of applications. While a typical LED lighting device has a substantial portion of its light emitted near a normal to the semiconductor photonic chip emitting the light, the present approach may suitable provide a compact, easily manufacturable device with good thermal design characteristics and a changed emission pattern without changing the horizontal mounting plane of the semiconductor photonic chip.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to improvements in light emitting diode (LED) packaging and lighting devices. More particularly, the invention relates to advantageous techniques for directing LED output light. 
   BACKGROUND OF THE INVENTION 
   As illustrated by  FIGS. 1A ,  1 B and  1 C, a common prior art LED mounting arrangement results in a substantial portion of the light output going in a direction parallel to a normal to the top surface of a semiconductor photonic chip  12  as seen in  FIG. 1B . As seen in  FIG. 1A , a top view of an LED  10 , the semiconductor photonic chip  12  is mounted on a substrate  14  which is in turn mounted on a bonding pad  16 . The chip  12  is encapsulated beneath an optical lens  18  which focuses the light emitted by the chip  12 . 
     FIG. 1B  shows a side view of LED  10  with a plurality of light rays relative to a normal, N, to the top surface of chip  12  illustrating the light emitted by chip  12  as it passes out of lens  18 . 
     FIG. 1C  shows an illustrative plot of the light emitted by LED  10  with the y-axis representing the intensity, I, and the x-axis representing the angle, θ, of the emitted light with respect to the normal, N, of  FIG. 1B . As illustrated in  FIG. 1C , a substantial portion of the light emitted from the LED is along or near the normal, N. Conversely, only a small percentage is emitted sideways. For further details of exemplary prior art LED packages with the bulk of the light intensity emitted near the normal, N, see, for example, the product literature for the XLamp™ 7090 from Cree, Incorporated, as well as that for the LumiBright Light Engine from Innovations in Optics, Inc. The Light Engine product employs a reflective cup which is asserted to direct three times more light into a useable cone angle. 
   While in some applications it will be recognized that such an emission pattern is advantageous, it will be recognized, however, that for other applications, as discussed further below, it will be desirable to change the light emission pattern. It will further be recognized that good thermal heat dissipation, and ease of manufacture with a small number of parts are also highly desirable. 
   SUMMARY OF THE INVENTION 
   To such ends, as addressed in greater detail below, aspects of the present invention address an LED packaging arrangement which may employ a low part count for ease of manufacture. Further aspects address an LED packaging arrangement having good thermal dissipation characteristics. Other aspects address an LED packaging arrangement and a process for making such a package which results in an LED lighting product with a substantial amount of its emitted light emitted in a direction other than normal to the photonic chip, such as sideways. 
   For example, according to one aspect of the invention, a light emitting diode lighting device comprises a semiconductor photonic chip mounted on a substrate and connected to positive and negative electrodes; a transparent medium having a substantially paraboloid top surface having a focal point, the transparent medium also having a recess to receive the semiconductor photonic chip, wherein the focal point of the paraboloid top surface is substantially centered at the center of the top of the semiconductor photonic chip; and a mirrored surface substantially mating with said paraboloid top surface. It will be recognized as discussed further below, that multiple photonic chips may be employed in place of the single photonic chip in which case those multiple chips are clustered about the focal point. 
   According to another aspect of the invention, a method of making a light emitting diode lighting device comprises mounting a semiconductor photonic chip on a substrate; connecting the semiconductor photonic chip to positive and negative electrodes; and positioning a transparent medium having a substantially paraboloid top surface having a focal point above the semiconductor photonic chip so that a recess receives the semiconductor photonic chip, and the focal point of the paraboloid top surface is substantially centered at the center of the top surface of the semiconductor photonic chip; and providing a mirrored surface substantially mating with said paraboloid top surface. 
   As a further example of another aspect of the invention, an array of light devices comprising at least one emission enhanced light emitting diode lighting device comprising: a semiconductor photonic chip mounted on a substrate and connected to positive and negative electrodes; a transparent medium having a substantially paraboloid top surface having a focal point, the transparent medium also having a recess to receive the semiconductor photonic chip, wherein the focal point of the paraboloid top surface is substantially centered at the center of the top surface of the semiconductor photonic chip; and a mirrored surface substantially mating with said paraboloid top surface. 
   Additionally, a light emitting diode lighting device comprising: a semiconductor photonic chip mounted on a substrate and connected to positive and negative electrodes; and a transparent medium having light redirecting top surface; and a mirrored surface substantially mating with the top surface which redirects a substantial portion of any light emitted by the semiconductor photonic chip away from a normal to the semiconductor photonic chip, the transparent medium also having a recess to receive the semiconductor photonic chip, wherein the light redirecting top surface is positioned above the center of the top of the semiconductor chip. 
   These and other advantages and aspects of the present invention will be apparent from the drawings and Detailed Description which follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A-1C  are top and side views illustrating aspects of a prior art LED packaging arrangement, and a graph illustrating how the intensity of light emission tends to vary with the angle from normal, respectively; 
       FIG. 2  shows a perspective view of a mounting arrangement for mounting a semiconductor photonic chip on a substrate; 
       FIGS. 3A and 3C  show exemplary reflective members suitable for use in conjunction with the mounting arrangement of  FIG. 2  for 360° sideways emission, and 180° sideways emission, respectively, and  FIG. 3B  illustrates how sideways emission can be angled upwards or downwards by varying an angle φ with respect to the plane of mounting of the photonic chip; 
       FIG. 4  shows an exemplary LED assembly in accordance with the present invention combining the mounting arrangement of  FIG. 1  and the reflective member of  FIG. 3 ; 
       FIG. 5  is a flow chart of a method of making an LED assembly such as the exemplary LED assembly of  FIG. 4 ; 
       FIG. 6  shows an exemplary embodiment of a lighting application utilizing an LED light source in accordance with the present invention; 
       FIG. 7  shows an alternative exemplary embodiment of a lighting application utilizing an LED light source in accordance with the present invention; 
       FIGS. 8A and 8B  illustrate top and side views of an array of enhanced LED light sources in accordance with the present invention, while  FIG. 8C  shows a module or tile of multiple enhanced LED light sources for use in the array of  FIG. 8A ; 
       FIGS. 9A and 9B  show top and side views, respectively, of an alternative transparent medium; 
       FIG. 10  shows a perspective view of an alternative LED assembly; and 
       FIG. 11  shows a multiple photonic chip light source which may suitably be used in conjunction with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 2  shows a mounting arrangement  200  for mounting a semiconductor photonic chip  202  on a substrate  204  with conductive electrodes  206  and  207 , respectively. The conductive electrodes  206  and  207  may suitably be copper, for example. A bond wire  208  which may suitably be gold wire connects the semiconductor photonic chip  202  to the electrode  207 . The substrate  204  may suitably be a ceramic or a plastic, such as a liquid crystal polymer (LCP), which is a dielectric so that it is nonconductive. While plastic is presently preferred as a result of its low cost, it will be recognized other dielectrics may also suitably be employed. The plastic material is molded with electrodes which may be stamped or etched or it is initially laminated with copper which can then be etched to form the electrode arrangement shown in  FIG. 2 . Again, while copper is presently preferred, it will be recognized that other electrode materials and shapes may be employed so long as suitable current conduction is achieved at an acceptable cost. The copper electrodes may be overcoated with a highly reflective material, such as silver or aluminum. 
     FIG. 3A  shows a cross-sectional view of a reflecting member  300  along line  3 A- 3 A of  FIG. 4  which may be suitably used in conjunction with the mounting arrangement  200  to form an LED assembly  400  (shown in  FIG. 4 ) having a substantial sideways emission component in accordance with the present invention as discussed further below. The reflective member  300  has a reflective bottom surface  302  which is preferably a paraboloid surface. By this, it is meant that surface  302  may be envisioned as the surface formed when a parabola, P, is rotated 360° around a focal point, f, in a plane including line l parallel to top surface  304  of reflective member  300 . For the member  300  as seen in  FIG. 4 , the rotation is 360°, but as discussed further below the angle of rotation can be less as desired. For the sake of illustration, the lines representing the surface  302  at the cross-sectional face of member  300  have been extended in dashed lines so parabola, P, can be more readily visualized. It will be recalled that any light emitted from the focal point, f, of a reflective parabola, P, will be reflected sideways parallel to the line, l. Exemplary rays, r 1  and r 2  are shown to illustrate this reflection principle. Light emitted from near the focal point will be substantially reflected parallel to the line, l. 
   While a paraboloid reflective surface is presently preferred, it will be recognized that other reflective surfaces may be employed. For example, if ease and reduced cost of manufacturing are considered more important than the effectiveness of the redirection of the emitted light, it will be recognized that a simple surface to manufacture such as an inverted triangle, pyramid or the like may be employed. 
   As noted above, with line l bisecting parabola P, light will be substantially reflected by reflective parabola P parallel to line l. However, it will be further recognized that parabola P can also be rotated about focal point, f, in a plane through l and perpendicular to top surface  304  so that light will be reflected principally at an angle φ above or below the line l.  FIG. 3B  shows parabola P rotated by the angle φ in the plane through line l and perpendicular to top surface  304 . The plane of line l is also preferably the plane of mounting of the photonic chip as discussed further below. Now a reflective surface P′ reflects rays such as r 3  parallel to line l′. Thus, it is seen by varying the angle φ in a lighting device as shown in  FIG. 4 , for example, easy adjustability of the light emission characteristics can be achieved without varying the mounting of the photonic chip. 
   Member  300  may be satisfactorily formed in a number of manners. For example, it can be stamped from a metal sheet and then plated with silver or aluminum. Alternatively, it may be molded from plastic or glass with a bottom surface  302  having a fine finish and metallized with silver or aluminum so that the end result is a specular mirror surface. 
   As will be further discussed below in connection with  FIGS. 4-7 , while in some applications it is desirable to have 360° sideways illumination, where 180°, 90°, or any angle less than 360° sideways illumination is desired, the parabola P only needs to be rotated through the desired degree of rotation. So for 180° sideways illumination, parabola P is rotated 180° to establish a mirrored front surface and a solid mirrored back surface is created as seen in  FIG. 3C  for 180° member  310 . Other surfaces other than parabaloid can be similarly rotated from 10° to 360°, for example. 
     FIG. 4  shows a perspective view of LED assembly  400 . As seen in  FIG. 4 , reflective member  300  of  FIG. 3A  has been joined with a transparent medium  402  as discussed further below and mounted on the substrate assembly  200  of  FIG. 2  to form an exemplary sideways enhanced emission LED assembly  400  in accordance with the present invention. In this arrangement, the center of the top surface of the semiconductor photonic chip  202  is located substantially at the focal point, f, of parabola P of  FIG. 3A . It will be recognized that chip  202  has a top surface with an area such as 1 mm×1 mm so that it is not a point, but by locating the center of the top surface of this chip near the location of the focal point, a highly effective sideways emission will be achieved. In  FIG. 4 , solid surface line  302  represents a 360° reflective surface while dashed extension  302   a  represents a 180° rotated paraboloid surface as discussed in conjunction with  FIG. 3C  above. 
   The transparent medium  402  may be clear or may be colored or tinted to lend emitted light a desired color. It may be made from silicone, molded plastic, or glass, for example. It is presently preferred that medium  402  have a Shore hardness of approximately 10 through 70 on the D scale. Medium  402  also has a top surface which closely mates with the bottom reflective surface  302  of the reflective member  300 . The two pieces are joined together, for example, by a clear adhesive, such as silicone, for example. As an alternative for a two piece construction, the top surface of medium  402  may simply have a reflective coating, such as silver or aluminum coating applied to it as discussed further below in conjunction with the discussion of  FIGS. 9A and 9B . 
   The bottom surface of transparent medium  402  preferably has a recess located over the semiconductor photonic chip  202  and its bond wire  208  which is preferably filled with a soft gel that protects chip  202  and wire  208  from different expansions and contractions of the different parts of assembly  400  as a result of the different coefficients of thermal expansion and contraction of the various components. A presently preferred gel will have a Shore hardness of approximately 30 on the 00 scale. If it is desired to increase the reflectivity of the electrodes  206  and  207 , they may be coated or plated with a thin coating of silver or aluminum. A very soft clear adhesive is preferably employed to adhere substrate  200  to the bottom surface of the medium  402 . 
   In a presently preferred approach, the reflective member  300  and transparent medium  402  are glued together with a transparent adhesive. The combined unit is then flipped over so the recess of the bottom surface of the transparent medium  402  is facing up. The recess is filled with the soft gel. The assembly  200  or the remainder of the bottom surface which is now facing up is coated with adhesive. Then, substrate  200  is turned over and aligned with the bottom surface and the two parts are pressed together. 
     FIG. 5  shows an exemplary process  500  of making an LED assembly, such as the assembly  400  of  FIG. 4 . In step  502 , a semiconductor photonic chip is mounted on a substrate with electrodes to form a substrate assembly. In step  504 , an adhesive is selectively applied to the top surface of the substrate assembly. Before, in with parallel or afterwards, in step  506 , a reflective member having a bottom reflective surface is adhered to a transparent medium to form an integral piece. As the transparent medium has a recess to receive the semiconductor photonic chip, in step  508 , the integral piece is turned over so that its bottom surface faces up and a soft gel to protect against expansion and contraction flowing from different coefficients of thermal expansion and contraction of materials is placed in the recess. In step  510 , the substrate assembly is aligned with the integral piece and pressed together therewith and the adhesive is allowed to cure. While an exemplary process is described, it will be recognized that many variations therein will be apparent to those of ordinary skill in the art based upon the teachings herein, the wide variety of lighting applications to be addressed, and subsequent improvements in the art relative to materials such as adhesives, plastics, glasses and other components used to form light devices. 
   In a presently preferred embodiment, the bottom reflective surface is a paraboloid and the semiconductor photonic chip is located substantially at the focal point of the paraboloid. While a paraboloid surface is recognized as highly effective in directing light sideways, it will be recognized that a straight line surface, such as an inverted triangle or pyramid, substantially paralleling a tangent of such a surface will work; however, less effectively. 
   As a further step of method  500 , a substrate with copper electrodes may be plated with silver or aluminum to increase the reflectivity of the top surface of substrate assembly. 
     FIGS. 6-8  illustrate various exemplary applications for LED assemblies utilizing the teachings of the present invention.  FIG. 6  illustrates schematically a parking lot  610  with a large number of lights  620  on tall poles  630 . The lights along one edge of the parking lot  610  are shown representatively while other lights are simply indicated with an “x” to mark their location. A walkway  640  is shown extending from the parking lot  610  and leading to an event center  650 , such as a museum. Alongside the walkway  640  are a plurality of low lights  660  at knee height or lower to light the walkway. 
   While the lights  620  represented by an “x” might be good candidates for a 360° sideways light assembly in accordance with the present invention, the lights  620  shown at the top edge of the parking lot  610  are a good candidate for a 180° sideways light assembly in accordance with the present invention. This desirability of application is particularly appropriate in the case where a housing development has grown up just on the other side of a lightly forested area between it and the parking lot  610 . By more efficiently directing the emitted light inward towards the parking lot, the present invention helps the parking lot&#39;s owner to be a better neighbor. 
     FIG. 7  shows an exemplary application of a 90° sideways enhanced emission LED light source  720  in accordance with the present invention.  FIG. 7  shows schematically a corner mounting arrangement for a light in a room  710 . It will be apparent that more light emitted in a 90° radius from the corner in which light source  720  is mounted will be advantageous. 
     FIGS. 8A and 8B  show a perspective view and side view, respectively, of a flat panel back lighting arrangement  800  in accordance with the present invention.  FIGS. 8A and 8B  illustrate aspects of an array  810  of light devices for backlighting a flat panel liquid crystal display  800 . The array  810  comprises an N×M matrix of light devices one or more of which may be sideways enhanced LEDs in accordance with the invention, such as LEDs  810   N3 ,  810   N4 ,  810   N5  shown schematically in  FIG. 8B . It will be recognized that corner LEDs may have the 90° enhancement discussed above. Edge LEDs may have 180° enhancement and middle LEDs may have 360° enhancement. Also, upwards angling may be advantageously employed to achieve a desired overlap. 
     FIG. 8C  shows a module or tile arrangement  820  in which a 4×2 array of LEDs  821 ,  822 ,  823 ,  824 ,  825 ,  826 ,  827  and  828  is shown mounted on a common substrate  830 , such as a printed circuit board. Each of the four LEDs defining a column,  821 ,  822 ,  823 , and  824 ; and  825 ,  826 ,  827  and  828 , respectively, may be electrically serially connected while the two columns are electrically connected in parallel. Alternatively, it will be recognized that other electrical connections may be chosen depending upon the application. Some or all of the LEDs  821 - 828  may suitably be enhanced LEDs as taught herein. It will be recognized that a module or tile arrangement could vary in the number of rows, columns and total number of LEDs as desired for a particular application, and that arrangement  820  is merely exemplary. With modules or tiles, it will be recognized that LEDs on an edge might be 180° enhanced and corner modules might have 90° enhancement. 
     FIGS. 9A and 9B  show top and side views, respectively, of an alternative embodiment of a transparent medium  900  providing both emission along the normal and sideways as discussed further below. The transparent medium  900  has a 360° paraboloid top surface  902  as discussed above. As previously discussed, the focal point is substantially centered at the center of the top of semiconductor photonic chip  912  in a finished device. The top surface  902  also has a plurality of reflectively coated and clear bands  910 ,  930  and  950  and  920 ,  940  and  960 , respectively. The reflective bands  910 ,  930  and  950  result in an enhanced sideways emission while the clear bands  920 ,  940  and  960  allow a portion of the light intensity emitted by the photonic chip to be emitted upwards. For example, as seen in  FIG. 9B , first ray r 10  is reflected sideways by reflective band  930  while second ray 11  passes upwards through clear band  920 . It will be recognized that by controlling the widths and shapes of the bands  910 - 960  improved control and design of patterns of light emission can be achieved. 
     FIG. 10  shows a perspective view of an alternative LED assembly  1000 . As seen in  FIG. 10 , a reflective member  1050  has been formed as discussed further below and mounted on a substrate assembly, like substrate assembly  200  of  FIG. 2 , to form a further exemplary LED assembly  1000  in accordance with the present invention. In this arrangement, the center of the top surface of a semiconductor photonic chip  1002  is located substantially at the focal point f, of a parabola, such as parabola P of  FIG. 3A , but as will be discussed further below the parabola of  FIG. 10  is truncated when compared to parabola P. It will be recognized that chip  1002  has a top surface with an area such as 1 mm×1 mm so that it is not a point, but by locating the center of the top surface of this chip near the location of the focal point, a highly effective sideways emission will be achieved. 
   A transparent medium  1052  may be clear or may be colored or tinted to lend emitted light a desired color. It may be made from silicone, molded plastic, or glass, for example. In this embodiment, it is presently preferred that medium  1052  be made of glass. Medium  1052  has a top surface which is flat over most its extent, but has a portion  1054  which is paraboloid. The paraboloid portion  1054  is centered above the center of the top surface of photonic chip  1002  and extends a desired predetermined distance beyond the outer boundary of photonic chip  1002 . For example, if photonic chip  1002  has top surface area of 1 mm×1 mm, then the paraboloid surface may extend 2 mm or further out from point  1055 . Surface  1054  has a reflective coating  1056 . On top of medium  1052 , there is a flat layer of glass  1059  having an index of reflection different from that of medium  1052  so that incident light at an angle less than the critical angle is internally reflected and directed sideways out the sides of medium  1052  with high efficiency in a manner similar to that observed in optical fiber light transmission. The two pieces  1052  and  1059  are joined together, for example, by a clear adhesive, such as silicone, for example. As an alternative, the piece  1059  may have a paraboloid bottom surface mating with surface  1054  with this bottom surface having a silver or aluminum coating applied to it as discussed above. 
   The bottom surface of transparent medium  1052  preferably has a recess located over the semiconductor photonic chip  1002  and its bond wire  10 . This recess is preferably filled with a soft gel that protects chip  1002  and wire  1008  from different expansions and contractions of the different parts of assembly  1000  as a result of the different coefficients of thermal expansion and contraction of the various components. A presently preferred gel will have a Shore hardness of approximately 30 on the 00 scale. If it is desired to increase the reflectivity of electrodes  1006  and  1007 , they may be coated or plated with a thin coating of silver or aluminum. A very soft clear adhesive is preferably employed to adhere substrate  1000  to the bottom surface of the medium  1050 . 
   The reflective member  1052  and piece  1059  are glued together with a transparent adhesive to form a combined medium  1050 . The combined unit is then flipped over so the recess in the bottom surface of the transparent medium  1052  is facing up. The cored out portion is filled with the soft gel. The remainder of the bottom surface which is now facing up is coated with adhesive. Then, substrate  1000  is turned over and aligned with the bottom surface and the two parts are pressed together. It will be recognized a one piece medium  1050  could also be employed. 
   While the above discussion has focused on embodiments in which a single photonic chip is located under a reflective member, such as member  300 , it will be recognized that more than one photonic chip may be mounted on a substrate to increase the light emitted, to blend colors, or the like, and that multiple photonic chips may be located under a reflective member.  FIG. 11  shows a multiple photonic chip light source  1100  in which three chips  1112   1 ,  1112   2  and  1112   3  are mounted on a substrate  1114  which is in turn mounted on a bonding pad  1116 . An optional lens  1118  may be used to focus the light output. While three chips are shown for purposes of illustration, two, four or more chips might suitably be employed. In one embodiment, the multiple chips  1112   1 ,  1112   2  and  1112   3  replace single chip  202  in  FIG. 2 . In another embodiment, these multiple chips replace the chip  1002  in  FIG. 10 . In these arrangements, any chip or chips might not be located at the focal point of the parabola, but the chips would typically be clustered at or about this point. 
   While the present invention has been disclosed in the context of various aspects of presently preferred embodiments, it will be recognized that the invention may be suitably applied to other environments consistent with the claims which follow.