WO2006109113A2

WO2006109113A2 - Primary optic for a light emitting diode

Info

Publication number: WO2006109113A2
Application number: PCT/IB2006/000265
Authority: WO
Inventors: Vladimir Semenovich Abramov; Alexander Valerievich Shishov; Nikolay Valentinovich Scherbakov
Original assignee: Acol Technologies Sa
Priority date: 2005-04-12
Filing date: 2006-01-27
Publication date: 2006-10-19
Also published as: WO2006109113A3; WO2006109113A8

Abstract

A special reflector system is integrated with a cover element as part of an LED package. The device supports wavelength shifting medium and highly efficient light coupling to output beams including low divergence beams. The reflector is made at a surface which provides a high-low index mismatch to set up a total internal reflection in a conic section shaped area. The device permits direct on board mounting of semiconductor chips without having to provide for shaped recesses or ancillary reflector systems.

Description

Title: Primary Optic for a Light Emitting Diode

BACKGROUND OF THE INVENTIONS

Field

The following invention disclosure is generally concerned with light emitting systems and specifically concerned with package structures for high performance light emitting devices.

Prior Art

The prior art includes direct-on-circuit board structures where light emitting diodes, LEDs are fabricated on printed circuit board substrates and lenses being integrated therewith. However, those are characterized by their use of a reflector element which is problematic for manufacture. Since a semiconductor LED emits light from its side facets as well as its top surface, a considerable portion of light energy emanates orthogonal to the primary emission direction. In common LED packages, a reflector is used to turn light into the primary beam. These reflectors are sometimes formed as a metallic conic section into which the chip is soldered at its floor. Most common LEDs use this structure. Demand has recently come forth for LEDs fabricated in "on circuit board" systems. The LEDs are not constructed as self contained packages, but rather, they are built directly onto a circuit board which might be shared with other electronic devices and processes. When building an LED directly on a circuit board, special provision has to be made for a reflector. Where total light output is not a concern, the reflector may be simple omitted. Light from the semiconductor in a primary beam is used as output, and light from the sides of the chip is wasted. Where more efficient systems are needed, one must provide for some kind of reflector.

A reflector may be built into the circuit board as a recess therein. The circuit board may be prepared with circuit traces in a normal fashion. Thereafter, conic shaped recesses can be formed into the circuit board material and these recesses may be metalized; i.e. thin films of polished metal may be deposited on the conic surface. Diodes mounted in these recesses will have an output beam comprised of both the primary beam and light from the chip side facets which is redirected by the reflector into the output beam. Usually a cover element including a lens is mounted just above this structure. Sometimes it is not desirable to form recesses in circuit boards and this approach is not preferred. One alternative is to build a pedestal onto the circuit board surface. Into the pedestal, one can form a reflector and mounting site for the semiconductor chip. When such arrangement is used, a special lens with a cavity large enough to accommodate the pedestal, chip and wire bonds is place over and affixed to the circuit board. This permits light from the chip sides to reflect from the pedestal reflector and enter the lens along with the primary beam to increase the total output.

In both cases where a reflector is used, it remains a problem to form a reflector. Additional materials and process steps are needed. It is therefore desirable to create a system where one can omit the extra steps and material needed to provide a reflector yet still capture and use the light from the sides of the LED chip.

While systems and inventions of the art are designed to achieve particular goals and objectives, some of those being no less than remarkable, these inventions have limitations which prevent their use in new ways now possible. Inventions of the art are not used and cannot be used to realize the advantages and objectives of the inventions taught herefollowing. It should be understood that all of the herein referenced materials provide considerable definition of elements of present inventions. Therefore, those materials including the patent application identified above are incorporated herein by reference whereby this specification can rely upon them for enablement of the particular teachings of each.

SUMMARY OF THE INVENTIONS

Comes now, Abramov, V.S.; Shishov, A. V. and Scherbakov, N. V. with inventions of special light emitting diode packages including devices having integrated reflectors.

Systems presented in these disclosures include a special optical cover element having integrated therewith a novel reflector system. A highly specialized reflector is formed directly into material from which a cover element is made. In some best versions, a total internal reflector is formed as a polished surface of the cover element. This TIR reflector surface is well designed to couple with the sides of a light emitting semiconductor die which it is used in conjunction with. A cover element additionally is used as the primary lens for an LED packaging system. The top surface is generally shaped as a spherical boundary which further concentrates output from the chip.

Cover elements of these inventions may also include alignment and coupling means. An indexing means is formed with the molded cover element which permits it to join with a base substrate to form a complete package. The undersurface of the cover element may also include a flat alignment ridge to further assure good alignment coupling between the reflector and the semiconductor chip.

Objectives of these Inventions

It is a primary object of these inventions to provide new packages for light emitting diodes.

It is an object of these inventions to provide improved light capture optical systems in light emitting diode packages. It is a further object to provide a reflector which can be used with direct on circuit board LED systems. It is an object of these inventions obviate the need for constructing a metallic reflector on a circuit board.

A better understanding can be had with reference to detailed description of preferred embodiments and with reference to appended drawings. Embodiments presented are particular ways to realize these inventions and are not inclusive of all ways possible. Therefore, there may exist embodiments that do not deviate from the spirit and scope of this disclosure as set forth by appended claims, but do not appear here as specific examples. It will be appreciated that a great plurality of alternative versions are possible.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and drawings where Figure 1 illustrates a first version of devices of these inventions;

Figure 2 is another version having a special wavelength shifting - heat management medium;

Figure 3 is a ray trace diagram to suggest some optical paths which couple light into a primary beam; Figure 4 is another such ray trace diagram to suggest optical paths;

Figure 5 is another version which illustrates a special TIR reflector with a semiconductor light emitter; and

Figure 6 shows another version having discrete optical paths of different optical components.

PREFERRED EMBODIMENTS OF THESE INVENTIONS

In accordance with each of preferred embodiments of these inventions, there is provided a light emitting diode and package apparatus. It will be appreciated that each of the embodiments described include an apparatus and the apparatus of one preferred embodiment may be different than the apparatus of another embodiment. For purposes of this disclosure, a "light emitting diode and package" is a light source system comprised of both a semiconductor diode light emitter and an optomechanical and electronic package to provide electronic and mechanical support as well as optical coupling. A package includes at least a cover element and a substrate. The cover element defines, by its shape, several optical components or elements which in some versions forms a compound optical system with a plurality of paths. A substrate is arranged to provide mechanical coupling to the cover element and additionally to providing mounting and electronic support to the semiconductor chip. In some versions, a cover element and substrate are related to each other via cooperating indexing means which may be used to fasten these elements together as well as provide alignment and positioning functionality.

These inventions are particularly concerned with packages including a single piece cover element having a reflector integrated therewith. The cover element may be formed of a hard transparent material such as molded polymer. Some polymers suitable for making optical elements become quite fluid and pliable at high temperature. Material in such state may be injection molded and cooled to form a hard and durable clear plastic piece.

Sometimes this cover element is formed with a reflector on its undersurface. Particularly, some preferred versions include reflectors of a special nature; i.e. those of the total internal reflection TIR type configuration. A TIR reflector is created where a flat surface of the cover element forms an interface with air whereby light propagating inside the material from which the cover is made strikes the TIR surface at a sufficiently high angle and is 100% reflected therefrom said surface and remain in the cover element. Accordingly, TIR reflectors are formed integrally with the cover element as a flat molded surface. In this way, the LED package does not require a separate metallic cup or reflection surface. Indeed, these TIR reflectors may not include metal at all.

Because this innovative system has a very efficient geometry, a chip may be mounted directly to a circuit board or other substrate which does not support having a recessed reflector cut therein. There is no need to build bulky metallic structures about the chip to couple side emitted light upward. Since the reflector is integrated with the cover element, manufacture processes associated with prior art metal type reflectors are completely eliminated.

To gain a more complete understanding, the following descriptions refer to the appended drawings which illustrate the best modes of these inventions. Specifically, Figure 1 illustrates a favored version. A flat substrate 1 is coupled to a cover element 2 by way of melted plastic indexing means 3. In this instance, cylindrical 'pins' are formed with the cover element in a molding process. To join the cover element to the substrate, the pins are pushed into well placed and shaped holes in the substrate. The holes having a countersunk recess receive the pins therein and the pins may be further melted to fill the countersunk recess/cavity thus holding the cover element to the substrate in a firm and permanent fashion. The top of the cover element is a spherical surface 4 which provides a first system lens. A cavity or plurality of cavities 5 is formed between the cover element and the substrate when these two are joined. In at least one of these cavities, a semiconductor chip 6 may be mounted. The balance 7 of the cavity may be filled with air. In some cases, a second system lens 8, a curved spherical surface is formed in the undersurface of the cover element.

Significantly, the undersurface of these cover elements also provides a very special reflector system 9. An axially symmetric surface is formed as a conic section. The high index of refraction of the material from which the cover element is made forms an interface with air having a low index of refraction. This combination, a high-to-low index interface, sets up a perfect total internal reflection mirror. Light from the semiconductor die necessarily falls incident on the surface from the inside of the cover element material. As such, the light will be deflected upwardly towards the system primary lens. Light from the semiconductor side facets is combined with the light from the dominant top surface in a single beam. The cover element also includes seating mechanism 10 a flat ridge formed in the cover element which assures good and proper alignment of the reflector and the lens when the cover is affixed to the substrate. The cavity between the cover element and the substrate also provides enough room for electrical support such as a wire bond 11. Another preferred version is illustrated in Figure 2. Figure 2 includes a device having a high density medium in one cavity and low density medium in another. Further, this system includes a pedestal to slightly raise the semiconductor emitter. In detail, a cover element 21 is a hard molded plastic material. The cover element is brought into contact with a substrate 22 to form a primary cavity 23 and a second cavity 24. The primary cavity may be rilled with a dense multi purpose medium configured manage heat transfer, mechanical stability and wavelength shifting. For example, a phosphor material mixed with a gel binder to form a suspension composite will transmit heat by conduction, will change the light wavelength, and will permit flexible material in which the semiconductor is free to expand and contract without putting pressure on the hard cover element. Pedestal 25 raises the semiconductor chip 26 a bit from the substrate. It this way, light from the sides of the chip is better coupled to the TIR reflector 27. Reflector 27 is a TIR surface because the secondary cavity 24 contains only air or other low index medium setting up a high-low index interface at the surface. The cover element is also preferably designed with a seating surface 28 which sets flush with the substrate to more perfectly orient the reflector with respect to the chip. Rays 29 indicate that light from the sides of the semiconductor die pass through the cavity, into the high index cover element, and land on the reflector TIR surface and get deflected upward toward the lens surface.

To reduce the number of parts used to form LED packages, it is sometimes desirable to omit the pedestal yet still collect most light from the semiconductor sides. In this case, a special mirror is formed on the top of the substrate to reflect downward traveling rays back upward. Figure 3 shows a substrate with a mirror thereon its top surface just under the semiconductor die. Cover element 31 combines with substrate 32 to form cavity containing semiconductor die 33 which is mounted atop a thin mirrored surface 34. Light rays 35 propagating downward reflect from the mirror and are directed back into the system and further to TIR reflector 36. Some rays 37 from the side of the chip hit the reflector directly without first going to the mirror.

It is useful to concentrate on other possible optical paths in these devices. One will see that several distinct routes are possible. Although there is but one output beam, light from various parts of the chip may experience routes where different optical elements are encountered by certain rays. For example, one ray might experience a lens/reflector/lens combination, while another ray might only traverse a lens/lens pair. Figure 4 illustrates. Substrate 41 having thereon cover element 42 encapsulates semiconductor die which emits light rays 44, 45, and 46. Light rays 44 start in the semiconductor die 47, leave its top surface, continue through a cavity 48, enter a first lens, pass through the cover element, and finally leave the device from the lens which is its top surface. Light ray 45 leaves a side facet of the semiconductor chip, passes through a cavity, through a first lens, then is reflected at TIR mirror 49, passes through the cover element and leaves the lens which is the top surface thereof. Ray 46 is similar.

Some system versions of particular interest have a discontinuity in one optical element which divides the two distinct optical trains. Figure 5 illustrates one such version. Cover element 51 is placed atop substrate 52. The cover element has an undersurface with a flat circular aperture 53, a TIR reflector 54, and a special cylindrically shaped entrance aperture surface 55. As in other versions, a cavity is formed into which a semiconductor die 57 is accommodated. In this version, light leaving the chip either passes through flat aperture 53 or cylindrical aperture 55. If light passes cylindrical aperture 55, then it also falls incident on the TIR reflector and is directed upward toward the top surface of the cover element. Light passing through the flat aperture 53 simply continues through the cover element and exits at the top surface lens. Optical engineers might notice that these two optical paths might cause the combined output beam to appear to come from two distinct point sources where one appears a bit further back that another due to the greater path length. Where such effect is to be avoided, another lens can be used to shift the apparent position of one source relative to the other. Figure 6 illustrates.

Substrate 61 and cover element 62 form the package for a light emitting system. Primary lens 63 in the top surface of the cover element is shared by both of two distinct optical trains. Light generated in semiconductor die 64 and passing, for example through its side facets, may enter cylindrical aperture 65 and reflect from conic section surface TIR reflector 66. Alternatively, light from the chip may leave its top surface, pass through curved undersurface lens 67, and continue to the top of the cover element. Lens 67 can be arranged with a curvature to improve the virtual location of the 'point' source so that it more closely corresponds to the point source of the other optical train. One will now fully appreciate how LED packages having high functioning multipurpose cover elements with integrated reflectors are realized. Although present inventions have been described in considerable detail with clear and concise language and with reference to certain preferred versions thereof including best modes anticipated by the inventors, other versions are possible. Therefore, the spirit and scope of the invention should not be limited by the description of the preferred versions contained therein, but rather by the claims appended hereto.

Claims

The following is claimed:

1) A light emitting diode and package light source system comprising: a substrate having at least one substantially flat surface; a semiconductor light emitting diode chip affixed to the substantially flat surface; and a hard transparent cover element comprising a lens and integrated reflector.

2) A light emitting diode and package light source system of claim 1, said reflector is a total internal reflection TIR type surface structure formed of a high- low optical index interface.

3) A light emitting diode and package light source system of claim 1, said reflector is formed of a polished metallic reflective layer.

4) A light emitting diode and package light source system of claim 2, said surface is formed in the shape of a conic section.

5) A light emitting diode and package light source system of claim 4, said conic section has a terminal edge which abuts with the substantially flat surface of said substrate to form an enclosed cavity between said cover element and said substrate.

6) A light emitting diode and package light source system of claim 1, said cover element is a molded plastic member.

7) A light emitting diode and package light source system of claim 6, said cover element is formed from a polymer material. 8) A light emitting diode and package light source system of claim 1, said cover element comprises two lenses and a reflector to form an optical train going from the light emitter, through a first lens, then to a reflector, and finally through a second lens.

9) A light emitting diode and package light source system of claim 1, said cover element comprises two lenses and a reflector to form two independent optical paths, a first going from a light emitter, through a first lens then through a second lens, another optical path going from a light emitter, through a cylindrical aperture of a cover element and then to a reflector, and finally through a second lens.

10) A light emitting diode and package light source system of claim 1, said cover element also includes a mechanical interlocking system which couples said cover element to said substrate.

11) A light emitting diode and package light source system of claim 10, said interlocking system is comprised of cooperating complementary mechanical alignment means of two parts, a first part being integrated with the cover element and a second part formed in said substrate, whereby when a cover is set to and coupled with a substrate, the lens is positioned and aligned such that the reflector and lens are well aligned with the emitter element.

12) A light emitting diode and package light source system of claim 11, said alignment means is further defined as a set of pins and holes, said pins when placed in said holes causes the cover element to become aligned with a semiconductor chip well placed on a substrate.

13) A light emitting diode and package light source system of claim 12, said pins have an end which is melted and reshaped after having been pushed through holes in the substrate to form a permanent fixture between cover element and substrate.

14) A light emitting diode and package light source system of claim 1, said cover element also includes a seat surface being a flat ridge which causes when joined with said substrate, the reflector to become optically coupled with the side facets of the semiconductor die.

15) A light emitting diode and package light source system of claim 5, said enclosed cavity is filled with a wavelength shifting medium having a high thermal index whereby heat is transmitted efficiently through said medium.