Flip-chip phosphor coating method and devices fabricated utilizing method

• US 20090179207A1
• Filed: 01/11/2008
• Published: 07/16/2009
• Est. Priority Date: 01/11/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Ibbetson, James, Keller, Bernd, Chitnis, Ashay
• Granted Patent: US 8,878,219 B2
• Time in Patent Office: Days
• US Class Current: 257/88
• CPC Class Codes: H01L 2224/13 of an individual bump connector
• CPC Class Codes: H01L 27/15 including semiconductor components having potential barriers, specially adapted for light emission
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 2933/0066 relating to arrangements for conducting electric current to or from the semiconductor body
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil
• 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
• CPC Class Codes: H01L 33/64 Heat extraction or cooling elements

Abstract

Methods for fabricating light emitting diode (LED) chips one of which comprises flip-chip mounting a plurality of LEDs on a surface of a submount wafer and forming a coating over said LEDs. The coating comprising a conversion material at least partially covering the LEDs. The coating is planarized to the desired thickness with the coating being continuous and unobstructed on the top surface of the LEDs. The LEDs chips are then singulated from the submount wafer. An LED chip comprising a lateral geometry LED having first and second contacts, with the LED flip-chip mounted to a submount by a conductive bonding material. A phosphor loaded binder coats and at least partially covers the LED. The binder provides a substantially continuous and unobstructed coating over the LED. The phosphor within the coating absorbs and converts the wavelength of at least some of the LED light with the coating planarized to achieve the desired emission color point of the LED chip.

Claims

1. A method for fabricating light emitting diode (LED) chips, comprising:

flip-chip mounting a plurality of LEDs on a surface of a submount wafer;

forming a coating over said LEDs, said coating comprising a conversion material at least partially covering said LEDs;

planarizing said coating to the desired thickness, said coating being substantially continuous and unobstructed on the top surface of said LEDs; and

singulating said LED chips from said submount wafer.

2. The method of claim 1, wherein at least some of said singulated LED chips comprise an LED, a portion of said coating, and a portion of said submount wafer, said coating at least partially covering said LED.

3. The method of claim 1, wherein said singulated LEDs chips comprise a portion of said coating, said portion being shaped or patterned.

4. The method of claim 1, wherein said LED chips emit white light.

5. The method of claim 1, wherein said LEDs have a lateral geometry and comprise n- and p-type layers, and further comprise first and second contacts on said n- and p-type layers respectively.

6. The method of claim 5, wherein said submount wafer comprises conductive vias, each of which is in electrical contact with one of said first and second contacts.

7. The method of claim 1, further comprising surface mount leads on said submount wafer.

8. The method of claim 1, wherein said submount wafer comprises a temporary carrier, wherein said method comprises the further step of removing said temporary carrier.

9. The method of claim 1, wherein said submount wafer comprises a lead frame.

10. The method of claim 1, wherein said LEDs are provided on a growth substrate.

11. The method of claim 10, further comprising removing at least a portion of said growth substrate prior to forming said coating.

12. The method of claim 10, wherein said substrate is shaped or textured.

13. The method of claim 1, wherein said step of forming a coating over said LEDs comprises providing a preformed coating layer and placing it over said LEDs.

14. The method of claim 1, further comprising curing said coating.

15. The method of claim 1, further comprising forming a surface texture on said coating.

16. The method of claim 1, further comprising forming a surface texture on said LED.

17. The method of claim 1, wherein said coating comprises a phosphor loaded binder.

18. The method of claim 17, wherein said phosphor loaded binder comprises multiple phosphors.

19. The method of claim 1, wherein said coating comprises scattering particles.

20. The method of claim 1, wherein said coating comprises multiple layers with different compositions.

21. The method of claim 17, wherein said binder comprises one of the materials from the group consisting of silicone, epoxy, glass, spin-on glass, BCB, polymides and polymers.

22. The method of claim 17, wherein said phosphor comprises a material from the group consisting of YAG:

Ce, Y₃Al₅O₁₂;

Ce (YAG), Tb_3-xRE_xO₁₂;

Ce (TAG);

RE=Y,Gd,La,Lu, and Sr_2-x-yBa_xCa_ySiO₄;

Eu.

23. The method of claim 1, wherein said coating covers said LEDs by one of the methods from the group consisting of spin coating, electrophoretic deposition, dispense, electrostatic deposition, printing, jet printing, screen printing and preform.

24. The method of claim 1, further comprising mounting one of said LED chips to a second submount or printed circuit board (PCB).

25. A light emitting diode (LED) chip wafer, comprising:

a submount wafer;

a plurality of LEDs having contacts accessible at one side and mounted to said submount wafer so that said contacts are accessible at said submount wafer; and

a phosphor loaded binder coating at least partially covering said LEDs and having substantially the same thickness over each of said LEDs and being continuous and unobstructed over each of said LEDs, at least some of the light emitted from said LEDs passing through said coating where at least some of said LED light is converted by the phosphor in said coating.

26. The LED chip wafer of claim 25, wherein at least some of said plurality of LEDs has lateral geometry.

27. The LED chip wafer of claim 26, wherein said at least some of said plurality of LED comprises oppositely doped layers with a mesa formed on one of said oppositely doped layers.

28. The LED chip wafer of claim 26, wherein said contacts comprise first and second contacts, the first being on said mesa of one of said oppositely doped layers and the second being on the other of said oppositely doped layers.

29. The LED chip wafer of claim 25, further comprising conductive vias through said submount wafer each of which is in electrical contact with one of said contacts.

30. The LED chip wafer of claim 41, wherein at least some of said LEDs have a textured surface that comprises texture features larger than 10% of the thickness of said LED.

31. The LED chip wafer of claim 25, wherein said submount wafer is capable of being separated into LED chips.

32. The LED chip wafer of claim 25, wherein said coating has a uniform thickness above said LEDs.

33. The LED chip wafer of claim 25, wherein said coating has a textured surface.

34. The LED chip wafer of claim 25, wherein said coating comprises multiple phosphors.

35. The LED chip wafer of claim 25, wherein said coating comprises scattering particles.

36. The LED chip wafer of claim 25, wherein said LEDs are made of. materials from the Group-III nitride material system.

37. The LED chip wafer of claim 25, wherein said submount wafer comprises a lead frame.

38. The LED chip wafer of claim 25, wherein said submount wafer comprises a temporary carrier.

39. The LED chip wafer of claim 25, wherein said LEDs are interconnected in an LED array.

40. The LED chip wafer of claim 25, further comprising a reflective layer formed integral to said substrate wafer.

41. The LED chip wafer of claim 25, wherein said coating comprises multiple layers with different compositions.

42. The LED chip wafer of claim 25, capable of emitting white light from said LEDs and coating.

43. A light emitting diode (LED) chip, comprising:

a lateral geometry LED having first and second contacts, said LED flip-chip mounted to a submount by a conductive bonding material, an electrical signal applied to said LED through said submount;

a phosphor loaded binder on and covering the top surface of said LED and providing a substantially continuous coating over said LED, said phosphor within said coating absorbing and converting the wavelength of at least some of said LED light, said coating planarized to achieve the desired emission color point of said LED chip.

44. The LED chip of claim 43, wherein said phosphor coating is continuous over the top surface of said LED and has a substantially uniform thickness.

45. The LED chip of claim 43, emitter a white light combination of LED light and light from said phosphor.

46. The LED chip of claim 43, wherein said substrate comprises electrically conductive vias in electrical coupled to said contacts to permit an electrical signal to be applied to said LED through said submout.

47. The LED chip of claim 43, wherein said submount comprises surface mount leads.

48. The LED chip of claim 43, wherein said submount comprises a lead frame.

49. The LED chip of claim 43, wherein said submount comprises a temporary carrier.

50. A light emitting diode (LED) package comprising:

an LED chip comprising an LED flip chip mounted on a submount, said submount comprising surface mount leads and conductive vias through said submount and in electrical contact with said LED, said LED chip further comprising a continuous phosphor loaded binder coating on and covering at least all of the top surface of said LED, said phosphor within said coating absorbing and converting the wavelength of at least some of said LED light, said coating planarized to achieve the desired emission color of said LED chip; and

a second submount having a plurality of package leads, said LED chip mounted to said second submount in electrical connection with at least one of said package leads.

51. The package of claim 50, further comprising and encapsulation at least partially surrounding said LED.

52. The package of claim 50, further comprising secondary optics directly on said LED.

53. The package of claim 50, emitting white light.