Laminating encapsulant film containing phosphor over LEDS

• US 20070096131A1
• Filed: 10/28/2005
• Published: 05/03/2007
• Est. Priority Date: 10/28/2005
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Chandra, Haryanto
• Granted Patent: US 7,344,952 B2
• Time in Patent Office: Days
• US Class Current: 257/99
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil
• CPC Class Codes: H01L 33/52 Encapsulations

Abstract

A process is described for wavelength conversion of LED light using phosphors. LED dies are tested for correlated color temperature (CCT), and binned according to their color emission. The LEDs in a single bin are mounted on a single submount to form an array of LEDs. Various thin sheets of a flexible encapsulant (e.g., silicone) infused with one or more phosphors are preformed, where each sheet has different color conversion properties. An appropriate sheet is placed over an array of LED mounted on a submount, and the LEDs are energized. The resulting light is measured for CCT. If the CCT is acceptable, the phosphor sheet is permanently laminated onto the LEDs and submount. The lamination encapsulates each LED to protect the LEDs from contaminants and damage. The LEDs in the array of LEDs on the submount are separated. By selecting a different phosphor sheet for each bin of LEDs, the resulting CCT is very uniform across all bins.

Claims

1. A method of fabricating a light emitting diode (LED) comprising:

providing a plurality of groups of LEDs, each group of LEDs producing a different range of peak wavelengths determined by testing;

mounting a plurality of LEDs of a single particular group onto a submount;

providing a plurality of different wavelength-conversion sheets, each sheet comprising a phosphor combined with a flexible encapsulate material, each sheet having a different phosphor conversion characteristic;

selecting a particular one of the wavelength-conversion sheets for applying over the LEDs on the submount;

energizing one or more LEDs on the submount;

detecting an emitted color generated by the combination of the energized one or more LEDs and the particular wavelength-conversion sheet to ensure the emitted color meets a predetermined color; and

encapsulating LEDs from the single particular group mounted on a submount with the particular wavelength-conversion sheet if the emitted color meets the predetermined color.

2. The method of claim 1 wherein each LED within a group of LEDs generates blue light.

3. The method of claim 1 wherein each LED within a group of LEDs generates UV light.

4. The method of claim 1 further comprising selecting a different wavelength-conversion sheet if, during the step of detecting an emitted color, the detected color does not match the predetermined color.

5. The method of claim 1 wherein the predetermined color is a particular color temperature for white.

6. The method of claim 1 wherein there is one or more different wavelength-conversion sheets for each group of LEDs.

7. The method of claim 1 wherein the range of peak wavelengths in each group is between about 3 and 10 nm.

8. The method of claim 1 wherein the different wavelength-conversion sheets differ by different weight ratios of phosphor to encapsulant or different thicknesses of the sheets.

9. The method of claim 1 wherein a thickness of each wavelength-conversion sheet is between about 50-200 microns.

10. The method of claim 1 wherein there are different types of phosphors in a wavelength-conversion sheet.

11. The method of claim 1 wherein encapsulating the LEDs comprises heating the selected wavelength-conversion sheet while pressing it over the LEDs.

12. The method of claim 1 wherein encapsulating the LEDs comprises heating the selected wavelength-conversion sheet while over the LEDs and providing a vacuum between the sheet and the submount.

13. The method of claim 1 wherein there are multiple wavelength-conversion sheets associated with each group of LEDs.

14. The method of claim 1 wherein encapsulating the LEDs results in the predetermined color being substantially achieved for all groups of LEDs by combining any group of LEDs with a particular one of the different wavelength-conversion sheets.

15. The method claim 1 further comprising separating encapsulated LEDs from other LEDs mounted on the submount.

16. The method of claim 1 wherein the submount provides electrical contacts for energizing the LEDs on the submount.

17. The method of claim 1 wherein providing a plurality of different wavelength-conversion sheets comprises depositing a liquid encapsulant containing a phosphor on a flat surface and spinning the flat surface until the encapsulant is of a desired thickness.

18. The method of claim 1 wherein providing a plurality of different wavelength-conversion sheets comprises depositing a liquid encapsulant containing a phosphor on a flat surface in a mold such that the encapsulant is of a desired thickness.

19. The method of claim 1 wherein the LEDs are GaN based LEDs.

20. The method of claim 1 wherein the phosphor generates yellow light.

21. The method of claim 1 wherein the phosphor comprises a plurality of phosphor materials and generates red and green light.

22. The method of claim 1 wherein the steps of energizing and detecting are performed only during formulation of the plurality of wavelength-conversion sheets and when determining which particular one of the wavelength-conversion sheets is to be associated with each group of LEDs.

23. A light emitting diode (LED) structure comprising:

one or more LEDs mounted on a submount, each LED on the submount emitting a peak wavelength within a predetermined range of peak wavelengths; and

a preformed encapsulant sheet, of uniform thickness, overlying and encapsulating each LED on the submount, the encapsulant sheet containing one or more types of phosphors for converting light emitted by each LED into light of a different wavelength.

24. The LED structure of claim 23 wherein the one or more LEDs mounted on a submount comprises an array of LEDs mounted on a submount, each LED in the array emitting a peak wavelength within a predetermined range of peak wavelengths.

25. The LED structure of claim 23 wherein the encapsulant sheet is one of a plurality of encapsulant sheets having different wavelength-conversion characteristics and selected based on a peak wavelength emitted by the one or more LEDs such that the combination of the one or more LEDs and the encapsulant sheet produces a certain predetermined color.

26. The LED structure of claim 23 wherein the combination of the LEDs and the encapsulant sheet has been tested prior to the encapsulant sheet being permanently affixed to the LEDs.

27. The LED structure of claim 23 wherein the encapsulant sheet has a substantially constant thickness, wherein the constant thickness is a substantially single thickness between 50-200 microns.

28. The LED structure of claim 23 wherein the encapsulant sheet comprises silicone.

29. The LED structure of claim 23 wherein the one or more LEDs are GaN based LEDs emitting blue or UV light.