FRAME BASED PACKAGE FOR FLIP-CHIP LED
A hollow frame is configured to surround the periphery of a substantially self-supporting flip-chip light emitting device. The frame may be shaped to also contain a wavelength conversion element above the light emitting surface of the light emitting device. The lower surface of the light emitting device, which is exposed through the hollow frame, includes contact pads coupled to the light emitting element for surface mounting the light emitting module on a printed circuit board or other fixture. The flip-chip light emitting device may include a patterned sapphire substrate (PSS) upon which the light emitting element is grown, the patterned surface providing enhanced light extraction from the light emitting element, through the patterned sapphire substrate.
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This application is a continuation of U.S. patent application Ser. No. 14/917,217 filed Mar. 7, 2016, which is a §371 application of International Patent Application No. PCT/IB2014/064106, filed Aug. 28, 2014, which claims the benefit of U.S. Provisional Application Ser. No. 61/877,434, filed Sep. 13, 2013 and 61/936,360, filed Feb. 6, 2014, the contents of which are hereby incorporated by reference herein.
FIELD OF THE INVENTIONThis invention relates to the field of light emitting devices, and in particular to a frame that provides a reflective enclosure about the periphery of the device.
BACKGROUND OF THE INVENTIONThe ever expanding use of semiconductor light emitting devices has produced a highly competitive market for these devices. In this market, performance and price are often significant for providing product distinction among vendors. Accordingly, a common objective is to reduce the cost of production while providing equivalent or better performance from the light emitting device.
One technique for providing relatively inexpensive packaging of a light emitting element is to place the light emitting element in a frame with leadframe contacts that facilitate external connections to the light emitting element. An LED leadframe generally comprises a pair of conductors that are shaped to provide for external connections to the LED. A support frame may be molded about the leadframe such that the leadframe conductors provide conductive surfaces within the support frame to mount the LED, and conductive surfaces at the exterior of the support frame to mount the framed LED on a printed circuit board or other fixture.
USPA 2010/0207140, “COMPACT MOLDED LED MODULE”, published 19 Aug. 2010 for Serge L. Rudaz, Serge Bierhuizen, and Ashim S. Hague, and incorporated by reference herein, discloses an array of support frames within which light emitting devices are bonded to leadframe contacts within each support frame, as illustrated in
The tub 10 may be subsequently filled with an encapsulant. Optionally, the encapsulant, or the protective coating 28, or the light emitting device 20, may include a wavelength conversion material, such as phosphor, that absorbs some or all of the emitted light and emits light at a different wavelength. The interior walls 15 of the tub 10 may be reflective, to redirect light toward the outside of the tub 10.
Upon completion, the individual light emitting modules 38 formed by the frame array 40 are singulated by slicing along the line 36. The individualized light emitting modules 38 include side surfaces 35 that facilitate the picking and placing of the light emitting module 38, but consume significantly more volume than the light-producing element 20, and introduces a substantially larger footprint compared to the surface area of the light-producing element 20. This substantial volume and footprint ‘overhead’ limits the use of such a light emitting module in applications such as flash or illumination elements for portable devices, such as smart phones and the like.
SUMMARY OF THE INVENTIONIt would be advantageous to provide a less complex process for providing a light emitting module with side surfaces that facilitate handling of the light emitting module and contacts opposite the light emitting surface. It would also be advantageous to provide such a light emitting module with minimal volume and footprint overhead.
To better address one or more of these concerns, in an embodiment of this invention, a hollow frame is configured to surround the periphery of a substantially self-supporting flip-chip light emitting device. The frame may be shaped to also contain a wavelength conversion element above the light emitting surface of the light emitting device. The lower surface of the light emitting device, which is exposed through the hollow frame, includes contact pads coupled to the light emitting element for surface mounting the light emitting module on a printed circuit board or other fixture. The flip-chip light emitting device may include a patterned sapphire substrate (PSS) upon which the light emitting element is grown, the patterned surface providing enhanced light extraction from the light emitting element, through the patterned sapphire growth substrate.
The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:
Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.
DETAILED DESCRIPTIONIn the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
Thick, self-supporting light emitting devices are now commonly available.
The substrate 110 may be sliced/diced (dashed lines in
To increase the light extraction efficiency from the light emitting element 120 into the substrate 110, the interface between the substrate 110 and light emitting element 120 may be ‘roughened’ to reduce the likelihood of total internal reflection (TIR) at the interface. Commonly, the substrate 110 is a Patterned Sapphire Substrate (PSS) upon which the light emitting element 120 is grown, the pattern on the sapphire substrate creating the aforementioned ‘roughened’ interface between the substrate 110 and the light emitting element 120.
Although the light emitting device 100 is substantially self-supporting, it generally may be ‘packaged’ to withstand subsequent handling as it undergoes the various processes during assembly of the final product, such as the assembly of a printed circuit board and other fixtures. As in the example of
The encapsulation serves multiple purposes; the encapsulant protects the light emitting chip from the environment, and may be formed to provide one or more particular optical functions. For example, the encapsulant may include wavelength conversion material, such as phosphor, that converts some or all of the light emitted from the light emitting chip 100 into light of a different wavelength. The encapsulant may also be shaped to form a lens that provides a desired light output pattern. Optionally, the encapsulant may be placed within a well formed by reflective walls, such as the tub 10 of the light emitting module 38 in
Although
Before assembly, the array 400 may be processed to apply a reflective material upon the walls 215 within each frame 210. Depending on the intended application for the packaged device, the entire array 400 may be spray coated with a reflective material, or the upper surface of the frames 210 may be masked while the reflective material is applied to the interior walls Other techniques may be used to apply the reflective coating, including clipping the array 400 in a vat of reflective material. In some embodiments, the material of the frame 210 may be inherently reflective, eliminating the need to apply a separate reflective coating.
After assembly, the array of frames is sliced/diced along cutting lines 410 to provide singulated packaged light emitting devices 200, as illustrated in
As shown in
The chip 100 may be secured within the frame 210 using any of a variety of techniques. If the frame 210 is pliable, the opening in the frame may be sized to provide a friction fit. Alternatively, the opening in the frame may be slightly larger than the chip 100, and the walls 215 on the frame 210 or the sidewalls of the chip 100 may be coated with an adhesive before the chip 100 is inserted into the frame 210. If the adhesive is reflective, the need to provide a reflective surface on the walls 215 may be eliminated.
In some embodiments, the frame 210 may be a shrinkable material, such as a heat-shrink material that is shrunk after the light emitting chip 100 (and optional cap 230, discussed below) is inserted into the frame 210. In some embodiments, laser slicing of the frame 400 (in
As shown in
The light emitting surface 115 of the light emitting chip 100, and the light emitting surface 235 of the cap 230 may be roughened or patterned to enhance the light emission efficiency by reducing the likelihood of total internal reflection (TIR) at these surfaces. Optionally, an interface material may be applied at the interface between the light emitting chip 100 and the cap 230, or between these elements and the reflective walls 215 to enhance the optical coupling between these elements.
As shown in
After attaching the chip 100 and optional cap 230 to the frame 210, the packaged device 200 will have a light emitting surface 235 (or surface 115 if the optional cap 230 is not included) as the ‘upper’ surface, and contact pads 130 on the ‘lower’ surface of the device 200. In this manner, a packaged light emitting device 200 is formed without the use of a leadframe or a submount.
As shown in
One of skill in the art will recognize that the frame 210 may include other features that facilitate the assembly process. For example, the opening in the frame 210 may include features that allow air bubbles to escape the frame 210 when the chip 100 and cap 230 are inserted, common in the art. In like manner, the frame 210 may include a material such as TiO2 or silicone between the cap 230 and the reflective walls 215 to reduce or eliminate “blue ring”, which may be caused when blue light exits the edges of the light emitting chip 100, without passing through a cap that includes wavelength converting material.
One of skill in the art will also recognize that the frame 210 may provide other functions in addition to protecting the light emitting chip 100 and providing a package with minimal volume and footprint overhead. For example, the material for frame 210 may be selected to provide high thermal conductivity, thereby extending the life of the device 200 by efficiently dissipating the heat generated by the light emitting chip 100, and the cap 230 if it includes a wavelength conversion material.
Although the invention is presented above using an example process wherein the light emitting chip 100 is inserted first, then the cap 230, one of skill in the art will recognize that the cap 230 may be inserted into the frame 210 first, followed by the light emitting chip; or, the cap 230 and light emitting chip 100 may be attached to each other, then inserted into the frame 210.
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One of skill in the art will recognize that a variety of forming and assembling techniques may be used to achieve a desired packaging construct. Some or all of the techniques shown in
Although the opening in the frame 210 is preferably shaped to correspond to the shape of the light emitting chip, which is typically rectilinear, to minimize the footprint of the resultant device 200 (or 201-206), other shaped openings may be provided. For example, because it is generally simpler to drill or bore circular holes through a material, cylindric or conic holes may be provided as illustrated in
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As noted above, the frame 400 of
In the example automotive lighting applications, the placement of the chips 100 within defined cavities in the frame provides for a simple method of achieving the high alignment precision that may be required for certain automotive lamps.
Although
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.
For example, although the figures illustrate a frame 210 that encloses all of the elements 100, 230, 240 it is possible to operate the invention in an embodiment wherein some or all of the cap 230 extends above the frame 210 and is shaped to provide a particular optical effect. For example, the cap 230 may be mushroom-shaped, the upper portion providing a wider distribution of the emitted light. In like manner, some or all of the optical element 240 may extend above the frame 210, and the cap 230 may encapsulate the portion of the optical element 240 extending beyond the frame 210. The cap 230 may also be omitted and the optical element 240 may be shaped to provide the aforementioned desired optical effect.
Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
Claims
1. A light emitting device comprising:
- a frame with an opening formed therethrough;
- a light emitting chip disposed within the opening, the light emitting chip comprising: a substrate, a light emitting element in contact with the substrate, the light emitting element comprising an active region between an n-type semiconductor and a p-type semiconductor, and at least a first contact pad and a second contact pad in contact with a surface of the light emitting element that is opposite the substrate, the first contact pad being coupled to the n-type semiconductor and the second contact being coupled to the p-type semiconductor; and
- a pre-formed cap disposed within the opening.
2. The light emitting device of claim 1, wherein the pre-formed cap is shaped to form a lens.
3. The light emitting device of claim 1, wherein the pre-formed cap includes wavelength conversion material.
4. The light emitting device of claim 1, wherein the opening defines one or more inner walls of the frame, and surfaces of the one or more inner walls are reflective.
5. The light emitting device of claim 4, further comprising one of TiO2 or silicone disposed between the one or more inner walls of the frame and the pre-formed cap.
6. The light emitting device of claim 1, further comprising a removable sheet, a bottom surface of the frame being disposed on the removable sheet, the light emitting chip being disposed within the frame such that at least the first contact and the second contact extend below the bottom surface of the frame or are level with the bottom surface of the frame.
7. The light emitting device of claim 1, wherein the light emitting chip and the pre-formed cap are disposed within the frame such that a surface of the substrate of the light emitting chip is adjacent a surface of the pre-formed cap such that the surface of the substrate that is adjacent the surface of the pre-formed cap is a light emitting surface of the light emitting chip and a surface of the pre-formed cap that is opposite the surface of the pre-formed cap that is adjacent the light emitting surface of the light emitting chip is a light emitting surface of the pre-formed cap.
8. The light emitting device of claim 7, wherein at least one of the light emitting surface of the pre-formed cap and the light emitting surface of the light emitting chip is roughened or patterned.
9. The light emitting device of claim 8, further comprising an interface material disposed between the pre-formed cap and the light emitting chip.
10. The light emitting device of claim 9, wherein the interface material has an index of refraction between an index of refraction of the light emitting chip and an index of refraction of the pre-formed cap.
11. The light emitting device of claim 7, wherein the opening defines one or more inner walls of the frame, and the one or more inner walls of the frame are shaped to include a step on which the pre-formed cap is disposed.
12. The light emitting device of claim 7, wherein the opening defines one or more inner walls of the frame, and each of the one or more inner walls of the frame includes a sloped portion adjacent the pre-formed cap.
13. The light emitting device of claim 1, wherein the opening and the frame have the same shape.
14. The light emitting device of claim 1, wherein the opening has a cylindrical shape.
15. The light emitting device of claim 14, wherein the light emitting chip is rectilinear and the pre-formed cap has a cylindrical shape.
16. The light emitting device of claim 15, wherein a diagonal of the light emitting chip is less than or equal to a diameter of the opening having the cylindrical shape.
17. The light emitting device of claim 16, wherein one or more spaces between the pre-formed cap and inner walls of the frame defined by the opening having the cylindrical shape are filled with a reflective material.
18. The light emitting device of claim 1, wherein the frame is formed from a pliable material, and the opening is sized to provide a friction fit with at least one of the light emitting chip and the pre-formed cap.
19. The light emitting device of claim 1, wherein the opening is larger than the light emitting chip, and an adhesive material is disposed between the light emitting chip and inner walls of the frame defined by the opening.
20. The light emitting device of claim 19, wherein the adhesive is reflective.
21. The light emitting device of claim 1, wherein the frame is formed from a heat-shrink material.
Type: Application
Filed: Jul 1, 2017
Publication Date: Oct 19, 2017
Applicant: Lumileds LLC (San Jose, CA)
Inventors: Stephen Andrew Stockman (Morgan Hill, CA), Marc Andre de Samber (Lommel), Oleg Borisovich Shchekin (San Francisco, CA), Norbertus Antonius Maria Sweegers (Lierop), Ashim Shatil Haque (Fremont, CA), Yourii Martynov (Geldrop)
Application Number: 15/640,482