LIGHT EMITTING DEVICE

• US 20090294780A1
• Filed: 05/27/2008
• Published: 12/03/2009
• Est. Priority Date: 05/27/2008
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: Intermatic Incorporated (Wpa Participações e Serviços SA)
• Inventors: Chou, Hsi-yan, Li, Yi-Qun, Su, Hwa
• Granted Patent: US 8,461,613 B2
• Time in Patent Office: Days
• US Class Current: 257/88
• CPC Class Codes: F21K 9/20 Light sources comprising attachment means
• 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 2224/48091 Arched
• CPC Class Codes: H01L 2224/49107 on the semiconductor or solid-state body
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H05B 33/12 Light sources with substantially two-dimensional radiating surfaces
• CPC Class Codes: H05K 1/0206 by printed thermal vias
• CPC Class Codes: H05K 3/284 for encapsulating mounted components H05K1/185 takes precedence

Abstract

A light emitting device comprises: a plurality of light emitting diodes and an insulating (low temperature co-fired ceramic) substrate with an array of recesses each for housing a respective one of the light emitting diodes. The substrate incorporates a pattern of electrical conductors that is configured for connecting the light emitting diodes in a selected electrical configuration and to provide at least two electrical connections on the floor of each recess. Light emitting diodes can be electrically connected to the electrical connections by at least one bond wire or by flip chip bonding. Each recess is filled with a transparent material to encapsulate each light emitting diode. The transparent material can incorporate at least one phosphor material such that the device emits light of a selected color and/or color temperature.

Claims

1. A light emitting device comprising a plurality of light emitting diodes and an insulating substrate having an array of recesses each for housing a respective one of the light emitting diodes, said substrate incorporating a pattern of electrical conductors configured for connecting the light emitting diodes in a selected electrical configuration and to provide at least two electrical connections on the floor of each recess and wherein each light emitting diode is connected to the at least two electrical connections.

2. The device of claim 1, wherein the packing density of light emitting diodes per unit area of substrate is in a range 30 to 100 per cm².

3. The device of claim 1, wherein light emitting diodes are electrically connected to the electrical connections by at least one bond wire.

4. The device of claim 1, wherein light emitting diodes are electrically connected to the electrical connections by flip chip bonding.

5. The device of claim 1, and further comprising a thermally conducting pad on the base of each recess for mounting a respective light emitting diode in thermal communication therewith.

6. The device of claim 5, wherein the substrate further comprises thermal vias for conducting heat from the thermally conducting pad to an exterior of the substrate.

7. The device of claim 1, and further comprising a substantially transparent material substantially filling each recess to encapsulate each light emitting diode.

8. The device of claim 7, wherein the transparent material is selected from the list consisting of:

a UV curable polymer;

a thermally curable polymer;

an epoxy; and

a silicone material.

9. The device of claim 7, and further comprising incorporating at least one phosphor material in the transparent material, said phosphor material being operable to absorb at least a part of the light emitted by its associated light emitting diode and to re-emit light of a different wavelength.

10. The device of claim 7, and further comprising providing at least one phosphor material overlying each recess, said phosphor material being operable to absorb at least a part of the light emitted by its associated light emitting diode and to re-emit light of a different wavelength.

11. The device of claim 1, wherein the light emitting diodes are connected in an electrical configuration selected from the groups consisting of:

connected in series;

pairs of light emitting diodes connected in parallel with opposing polarity;

groups of light emitting diodes connected in series and said groups connected in parallel with opposing polarity; and

being connected in a bridge configuration.

12. The device of claim 1 and further comprising a rectifier arrangement for enabling the light emitting diodes to be operated directly from an AC supply.

13. The device of claim 12, wherein components of the rectifier arrangement are housed in one or more recesses.

14. The device of claim 12, wherein the rectifier arrangement comprises four diodes connected in a bridge rectifier configuration and wherein the pattern of electrical conductors is configured such that the light emitting diodes are connected in series between the rectifying nodes of the bridge.

15. The device of claim 14, wherein the diodes are selected from the group consisting of:

silicon;

germanium;

silicon carbide; and

gallium nitride diodes.

16. The device of claim 1, wherein the insulating substrate is selected from the group consisting of:

a low temperature co-fired ceramic;

silicon; and

a high temperature polymer.

17. The device of claim 1, wherein the light emitting diode comprise a gallium nitride-based light emitting diode chip.

18. The device of claim 1, wherein the array of recesses is configured as a square array.

19. An AC light source comprising an elongate circuit board having a plurality of light emitting devices according to claim 1 mounted on and disposed along the length of the circuit board and an elongate substantially transparent enclosure, said circuit board being configured to fit within said enclosure.

20. An AC light source comprising a ring shaped circuit board having a plurality of light emitting devices according to claim 1 mounted on and configured as a circular array, a body to which the circuit board in mounted in thermal communication therewith and a connector for connecting the light source to an AC supply.