Flexible distributed LED-based light source and method for making the same

• US 8,322,882 B2
• Filed: 09/22/2010
• Issued: 12/04/2012
• Est. Priority Date: 09/22/2010
• Status: Active Grant

• Current Assignee: Bridgelux Incorporated
• Original Assignee: Bridgelux Incorporated
• Inventors: Ward, Calvin B.
• Primary Examiner(s): Neils, Peggy A.
• Application Number:
  US12/888,196
• Publication Number:
  US 20120068622A1
• Time in Patent Office: 804 Days
• Field of Search: 362/249.02, 362/249.04, 362/231, 362/800, 362/294, 257/88, 257/98, 438/26, 438/122, 422/26, 422/122
• US Class Current: 362/249.02
• CPC Class Codes: H01L 2224/2919 with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/49113 the connectors connecting different bonding areas on the semiconductor or solid-state body to a common bonding area outside the body, e.g. converging wires
• CPC Class Codes: H01L 2224/83 using a layer connector
• CPC Class Codes: H01L 2224/83862 Heat curing
• CPC Class Codes: H01L 2224/85 using a wire connector
• CPC Class Codes: H01L 2224/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• CPC Class Codes: H01L 24/29 of an individual layer connector
• CPC Class Codes: H01L 24/32 of an individual layer connector
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 24/49 of a plurality of wire connectors
• CPC Class Codes: H01L 24/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• 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: H01L 2924/01013 Aluminum [Al]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/07802 : not being an ohmic electrical conductor
• CPC Class Codes: H01L 2924/12041 : LED
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H01L 2924/207 : Diameter ranges
• CPC Class Codes: H01L 33/486 : adapted for surface mounting
• CPC Class Codes: H05K 1/021 : Components thermally connected to metal substrates or heat-sinks by insert mounting
• CPC Class Codes: H05K 1/189 : characterised by the use of a flexible or folded printed circuit H05K3/326 takes precedence
• CPC Class Codes: H05K 2201/09909 : Special local insulating pattern, e.g. as dam around component
• CPC Class Codes: H05K 2201/10106 : Light emitting diode [LED]

Abstract

A precursor structure for fabricating light sources, the light sources fabricated therefrom, and the method of fabricating the precursor structure are disclosed. A precursor substrate includes a flexible printed circuit board on which dies are bonded and a separation ridge. The flexible printed circuit board has a bottom heat-conducting layer, an insulating layer, and a circuit layer. The insulating layer and the circuit layer include a plurality of openings that expose the top surface of the heat-conducting layer. The separation ridge extends above the circuit layer and the dies and is configured to prevent contact with the dies and any structures constructed above the dies when the precursor substrate is in contact with a surface positioned over the die and in contact with the separation ridge. The structure is well suited for roll-to-roll processing equipment.

Claims

1. A precursor substrate comprising:

a flexible printed circuit board having a bottom heat-conducting layer, an insulating layer, and a circuit layer, said insulating layer and said circuit layer comprising a plurality of openings that expose a top surface of said heat-conducting layer, and said circuit layer comprising a plurality of electrical conductors;

a plurality of dies bonded to said heat-conducting layer in a corresponding plurality of said openings, each die comprising an LED that is electrically connected to one of said electrical conductors; and

a separation ridge extending above said circuit layer and said dies,

wherein said separation ridge is configured such that said precursor substrate can be rolled up in a predetermined direction to form a plurality of coils such that said separation ridge prevents said LEDs and any structures constructed above said LEDs, except said separation ridge, from contacting said bottom heat-conducting layer of said flexible printed circuit board on an adjacent layer in said coil.

2. The precursor substrate of claim 1 further comprising a layer of material over each of said dies, said separation ridge extending above said layer of material.

3. The precursor substrate of claim 2 wherein said LEDs generate light of a first wavelength and wherein said layer of material comprises a phosphor that converts light of said first wavelength to light of a second wavelength different from said first wavelength.

4. The precursor substrate of claim 1 wherein said heat-conducting layer comprises a ferromagnetic material.

5. The precursor substrate of claim 4 wherein said ferromagnetic material is magnetized.

6. The precursor substrate of claim 1 wherein a bottom surface of said heat-conducting layer comprises an adhesive covered by a removable protective sheet.

7. The precursor substrate of claim 1, wherein said plurality of dies are organized into a plurality of die groups, each die group comprising:

a plurality of LEDs, each LED being bonded to said top surface of said heat-conducting layer, each LED being connected to first and second group contacts that power said LED when a potential is applied between said first and second group contacts, said circuit layer being patterned such that said precursor substrate can be cut to provide a light source comprising an integer number of said die groups that are powered from first and second light source contacts.

8. The precursor substrate of claim 7 wherein each die group comprises a group driving circuit that converts electrical power received on said first and second light source contacts to power that is applied to said first and second group contacts.

9. The precursor substrate of claim 7 wherein said die groups are arranged in a two dimension array of die groups, said two-dimensional array being arranged in a plurality of rows and columns.

10. The precursor substrate of claim 7 wherein all of said die groups are identical to one another.

18. The precursor substrate of claim 1 wherein said separation ridge comprises first and second linear ridges extending in said predetermined direction, said LEDs being located between said first and second linear ridges.

11. A method for fabricating a light source, said method comprising:

providing a flexible printed circuit board having a bottom heat-conducting layer, an insulating layer, and a circuit layer, said insulating layer and said circuit layer comprising a plurality of openings that expose a top surface of said heat-conducting layer, and said circuit layer comprising a plurality of electrical conductors;

bonding a plurality of dies to said heat-conducting layer in a corresponding plurality of said openings, each of said dies comprising an LED;

connecting each of said dies to one of said electrical conductors;

providing a separation ridge structure extending above said circuit layer and said dies; and

rolling up said flexible printed circuit board in a first direction to form a plurality of coils such that said separation ridge prevents said LEDs and any structures constructed above said LEDs, except said separation ridge, from contacting said bottom heat-conducting layer of said flexible printed circuit board on an adjacent layer in said coil.

12. The method of claim 11 further comprising depositing a layer of material over said dies, said separation ridge extending above said layer of material.

13. The method of claim 12 wherein said LEDs generate light of a first wavelength and wherein said layer of material comprises a phosphor that converts light of said first wavelength to light of a second wavelength different from said first wavelength.

14. The method of claim 11 wherein said heat-conducting layer comprises a ferromagnetic material.

15. The method of claim 11 further comprising applying a layer of an adhesive covered by a removable protective sheet to said bottom surface of said heat-conducting layer.

16. The method of claim 11, wherein said dies are organized into a plurality of die groups, each die group comprising:

a plurality of LEDs, each LED being bonded to said top surface of said heat-conducting layer, each LED being connected to first and second group contacts that power said LED when a potential is applied between said first and second group contacts, said circuit layer being patterned such that said precursor substrate can be cut to provide a light source comprising an integer number of said die groups that are powered from first and second light source contacts.

17. The method of claim 16 further comprising cutting said flexible printed circuit board to provide a light source having an integer number of said die groups and said first and second light source contacts.