Solid state light sheet using thin LEDs for general illumination

• US 8,461,602 B2
• Filed: 01/31/2011
• Issued: 06/11/2013
• Est. Priority Date: 08/27/2010
• Status: Active Grant

• Current Assignee: Quarkstar LLC
• Original Assignee: Quarkstar LLC
• Inventors: Lerman, Louis, York, Allan Brent, Henry, Michael David, Steele, Robert, Ogonowsky, Brian D.
• Primary Examiner(s): Weiss, Howard
• Assistant Examiner(s): Rao, Steven
• Application Number:
  US13/018,330
• Publication Number:
  US 20110180818A1
• Time in Patent Office: 862 Days
• Field of Search: 257/88, 257/99, 362/147, 362/150, 362/178, 362/479
• US Class Current: 257/88
• CPC Class Codes: F21K 9/27 Retrofit light sources for lighting devices with two fittings for each light source, e.g. for substitution of fluorescent tubes
• CPC Class Codes: F21S 8/06 by suspension
• CPC Class Codes: F21Y 2103/10 comprising a linear array of point-like light-generating elements
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• 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 33/507 the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body
• CPC Class Codes: H01L 33/58 Optical field-shaping elements
• CPC Class Codes: H01L 33/60 Reflective elements
• CPC Class Codes: H01L 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls

Abstract

A solid state light sheet and method of fabricating the sheet are disclosed. In one embodiment, bare LED chips have top and bottom electrodes, where the bottom electrode is a large reflective electrode. The bottom electrodes of an array of LEDs (e.g., 500 LEDs) are bonded to an array of electrodes formed on a flexible bottom substrate. Conductive traces are formed on the bottom substrate connected to the electrodes. A transparent top substrate having conductors is then laminated over the bottom substrate. Various ways to connect the LEDs in series are described along with many embodiments. The light sheets may be formed to emit light from opposite surfaces of the light sheet, enabling it to be used in a hanging fixture to illuminate the ceiling as well as the floor. The light sheet provides a practical substitute for a standard 2×4 foot fluorescent ceiling fixture.

Claims

1. A lighting device comprising:

a first substrate;

a plurality of non-packaged light emitting diode (LED) dies, each LED die having at least a first die electrode and a second die electrode; and

a second substrate, wherein the first and second substrates are formed of a material sufficiently deformable to conform to at least a fraction of a thickness of a single LED die of the plurality of LED dies,

the plurality of LED dies being spaced apart from one another and arranged between the first and second substrates, wherein the first and second substrates are deformed to conform to the plurality of LED dies and contact each other between the spaced apart plurality of LED dies to separately encapsulate each of the plurality of LED dies,

wherein the first substrate has first connection locations electrically connected to first conductors formed on the first substrate, the first die electrode of associated LED dies being aligned with and electrically connected to an associated first connection location on the first substrate without wire bonds, and the second substrate has second connection locations electrically connected to second conductors formed on the second substrate, the second die electrode of associated LED dies being aligned with and electrically connected to an associated second connection location on the second substrate without wire bonds,

wherein portions of the first conductors and portions of the second conductors overlap and electrically connect where the first substrate contacts the second substrate to create a series connection of the plurality of LED dies without using wire bonds, and

wherein at least one of the first substrate and second substrate has light passing locations for outputting light emitted by the plurality of LED dies.

2. The device of claim 1, wherein the first connection locations are connected to the first die electrodes of the associated LED dies by a conductive paste.

3. The device of claim 1,

wherein the plurality of LED dies are vertical diodes having a cathode electrode as the first die electrode on a first die surface and an anode electrode as the second die electrode on an opposite die surface,

wherein at least some of the first conductors are connected to the cathode electrodes and at least some of the second conductors are connected to the anode electrodes,

wherein the first conductors align with the second conductors and connect an anode of a first LED die from among the plurality of LED dies to a cathode of a second LED die from the plurality of LED dies to connect the first and second LED dies in series.

4. The device of claim 1, wherein the thickness of each one of the plurality of LED dies is equal to or less than 200 microns.

5. The device of claim 1 wherein at least one of the first substrate and second substrate is less than 2 mm thick.

6. The device of claim 1 further comprising a phosphor over a surface of the first substrate to convert light emitted by the plurality of LED dies to white light.

7. The device of claim 1, wherein a first edge of the first substrate and a second edge of the second substrate are connected together so that the first edge of the first substrate and the second edge of the second substrate are aligned when they are brought together for sandwiching the plurality of LED dies between the first substrate and the second substrate.

8. The device of claim 3 further comprising an electrical connection causing a plurality of groups of series-connected ones of the plurality of LED dies to be connected in parallel.

9. A lighting device comprising:

a first substrate;

a plurality of non-packaged light emitting diode (LED) dies, each LED die having at least a first die electrode and a second die electrode; and

a second substrate formed of a material sufficiently deformable to conform to at least a thickness of a single LED die of the plurality of LED dies, wherein the first substrate is formed of another material sufficiently non-deformable to remain planar at least over a base of the single LED die,

the plurality of LED dies being spaced apart from one another and arranged between the first and second substrates, wherein the second substrate is deformed to conform to the plurality of LED dies and contact the first substrate between the spaced apart plurality of LED dies to separately encapsulate each of the plurality of LED dies,

wherein the first substrate has first connection locations electrically connected to first conductors formed on the first substrate, the first die electrode of associated LED dies being aligned with and electrically connected to an associated first connection location on the first substrate without wire bonds, and the second substrate has second connection locations electrically connected to second conductors formed on the second substrate, the second die electrode of associated LED dies being aligned with and electrically connected to an associated second connection location on the second substrate without wire bonds,

wherein portions of the first conductors and portions of the second conductors overlap and electrically connect where the first substrate contacts the second substrate to create a series connection of the plurality of LED dies without using wire bonds, and

wherein at least one of the first substrate and second substrate has light passing locations for outputting light emitted by the plurality of LED dies.

10. The device of claim 9, wherein the first connection locations are connected to the first die electrodes of the associated LED dies by a conductive paste.

11. The device of claim 9,

wherein the plurality of LED dies are vertical diodes having a cathode electrode as the first die electrode on a first die surface and an anode electrode as the second die electrode on an opposite die surface,

wherein at least some of the first conductors are connected to the cathode electrodes and at least some of the second conductors are connected to the anode electrodes,

wherein the first conductors align with the second conductors and connect an anode of a first LED die from among the plurality of LED dies to a cathode of a second LED die from the plurality of LED dies to connect the first and second LED dies in series.

12. The device of claim 11, further comprising an electrical connection causing a plurality of groups of series-connected ones of the plurality of LED dies to be connected in parallel.

13. The device of claim 9, wherein the thickness of each one of the plurality of LED dies is equal to or less than 200 microns.

14. The device of claim 9, wherein at least the second substrate is less than 2 mm thick.

15. The device of claim 9, further comprising a phosphor over a surface of the first substrate to convert light emitted by the plurality of LED dies to white light.