Phosphor position in light emitting diodes

• US 8,425,271 B2
• Filed: 08/16/2007
• Issued: 04/23/2013
• Est. Priority Date: 09/01/2006
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Hussell, Christopher P., Bergmann, Michael J., Collins, Brian T., Emerson, David T.
• Primary Examiner(s): Patel, Nimeshkumar
• Assistant Examiner(s): Hollweg, Thomas A
• Application Number:
  US11/839,562
• Publication Number:
  US 20080054279A1
• Time in Patent Office: 2,077 Days
• Field of Search: 313498-512, 445/24, 445/22, 445/23, 445/58
• US Class Current: 445/23
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48465 the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
• 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 2924/00014 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 33/486 adapted for surface mounting
• CPC Class Codes: H01L 33/508 having a non-uniform spatial arrangement or non-uniform concentration, e.g. patterned wavelength conversion layer, wavelength conversion layer with a concentration gradient of the wavelength conversion material
• CPC Class Codes: H01L 33/54 having a particular shape
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

A method of forming an LED lamp with a desired distribution of phosphor is disclosed. The method includes the steps of mixing a plurality of phosphor particles in an uncured polymer resin for which the viscosity can be controlled in response to temperature to form a substantially uniform suspension of the phosphor particles in the resin. The uncured resin is then placed into a defined position adjacent an LED chip and the temperature of the resin is increased to correspondingly decrease its viscosity but to less than the temperature at which the resin would cure unreasonably quickly. The phosphor particles are encouraged to settle in the lowered-viscosity resin to a desired position with respect to the LED chip, and the temperature of the resin is thereafter increased to the point at which it will cured and solidify.

Claims

1. A method of forming an LED lamp with a desired distribution of phosphor, the method comprising:

selecting a desired position of phosphor particles with respect to an LED chip;

selecting a particle size of a plurality of phosphor particles based on a viscosity of an uncured polymer resin in response to temperature changes and based on said desired position of the phosphor particles with respect to the LED chip;

mixing a plurality of phosphor particles in the uncured polymer resin for which the viscosity can be controlled in response to temperature to form a substantially uniform suspension of the phosphor particles in the resin;

placing the uncured resin into a defined position adjacent the LED chip;

increasing the temperature of the resin in a first step to a temperature that correspondingly decreases the viscosity of the resin without immediately curing the resin;

encouraging the phosphor particles to settle in the lowered-viscosity resin to the desired position with respect to the LED chip; and

in response to the phosphor particles having settled at the desired position, thereafter increasing the temperature of the substantially uncured resin in a second step to a temperature higher than the first step and at which it will cure and solidify in about two hours or less.

2. A method according to claim 1 comprising incorporating a resin that is less susceptible to photochemical reactions when exposed to light in the blue or higher energy portions of the electromagnetic spectrum.

3. A method according to claim 2 comprising incorporating a polysiloxane resin.

4. A method according to claim 1 comprising incorporating a phosphor with a particle size that will remain suspended in the resin at temperatures of about 40°

C. or less, but that will settle within a reasonable period of time when the viscosity of the resin decreases.

5. A method of forming an LED lamp according to claim 1 wherein the step of mixing the phosphor particles comprises mixing particles of cerium doped yttrium aluminum garnet in the uncured polymer resin.

6. A method of forming an LED lamp according to claim 5 comprising mixing phosphor particles with an average particle size of about six microns.

7. A method of forming an LED lamp according to claim 1, comprising mixing the phosphor particles and the uncured polymer resin at a temperature of between about 25°

and 40°

C. prior to the step of placing the resin into the defined position adjacent the LED chip; and

further comprising the step of increasing the temperature of the resin to between about 40° and

80°

C. following the step of placing the uncured resin into the defined position.

8. A method of forming an LED lamp according to claim 1 wherein the step of increasing the temperature of the resin to the point at which it will cure comprises heating the resin to a temperature of between about 100°

and 200°

C.

9. A packaged light emitting diode formed by the method of claim 1.

10. A display that incorporates a packaged light emitting diode according to claim 9.

11. A display according to claim 10 that incorporates the packaged light emitting diode in combination with a light guide.

12. A method according to claim 1, wherein increasing the temperature of the resin in the first step comprises increasing the temperature within a temperature range that has a maximum value of less than 100°

C.

13. A method according to claim 1, wherein selecting the particle size of the phosphor particles comprises selecting the particle size for controlling a migration of the phosphor particles during the first step.

14. A method according to claim 1, wherein increasing the temperature of the resin in the first step comprises increasing the temperature within a temperature range that has a maximum value of less than 100°

C. and a minimum value at room temperature.

15. A method according to claim 1, comprising selecting a time interval for permitting the phosphor particles to settle at the desired position.

16. A method according to claim 15, wherein the time interval has a minimum value of about 10 minutes and a maximum value of about 5 hours.

17. A method of forming an LED lamp according to claim 1 comprising mixing the phosphor particles and the uncured polymer resin at a temperature of between about 25°

and 40°

C. prior to the step of placing the resin into the defined position adjacent the LED chip.

18. A method of forming an LED lamp comprising:

selecting a desired position of the phosphor with respect to an appropriate lamp package;

selecting a particle size of a phosphor based upon an intermediate temperature that lowers a viscosity of a resin for a time sufficient for the phosphor to settle to the desired position without rapidly curing the resin;

selecting and mixing a combination of a phosphor and a resin into a suspension that will remain homogeneous at a temperature of about 40°

C. or less for a time interval sufficient to permit the suspension to be dispensed into the appropriate lamp package;

dispensing the homogeneous mixture of phosphor and resin into a lamp package;

orienting the lamp package in a manner that allows the phosphor to settle to a desired position when the temperature is raised to an intermediate higher temperature that lowers the resin viscosity;

raising the temperature to the intermediate higher temperature that lowers the resin viscosity for a time sufficient for the phosphor to settle to the desired position without rapidly curing the resin; and

in response to the phosphor having settled at the desired position, raising the temperature to a point at which the substantially uncured resin cures within between about 5 minutes and 5 hours with the phosphor in the desired position.

19. A method of forming an LED lamp according to claim 18 comprising mixing a combination of a cerium doped yttrium aluminum garnet phosphor and a polysiloxane resin into the homogeneous suspension.

20. A method of forming an LED lamp according to claim 19 comprising mixing a phosphor that has an average particle size of about six microns.

21. A method of forming an LED lamp according to claim 18 wherein the step of orienting the lamp package comprises orienting the lamp package in a manner that settles the phosphor over and on the LED chip.

22. A method according to claim 18 wherein the step of raising the temperature to a point at which the resin cures comprises raising the temperature to between about 100°

and 200°

degrees centigrade.

23. A method according to claim 18, wherein raising the temperature to the intermediate higher temperature comprises raising the temperature within a temperature range that has a maximum value of less than 100°

C.

24. A method according to claim 18 wherein selecting the particle size of the phosphor comprises selecting the particle size for controlling a migration of the phosphor during the step of raising the temperature to the intermediate higher temperature.

25. A method according to claim 18, wherein raising the temperature to the intermediate higher temperature comprises raising the temperature within a temperature range that has a maximum value of less than 100°

C. and a minimum value at room temperature.

26. A method according to claim 18, comprising selecting a time interval for permitting the phosphor to settle at the desired position.

27. A method according to claim 26, wherein said time interval has a minimum value of about 10 minutes and a maximum value of about 5 hours.

28. A method according to claim 18 wherein the step of mixing the phosphor and the resin is carried out at about room temperature.

29. A method according to claim 18 wherein the step of raising the temperature to the intermediate higher temperature comprises raising the temperature to between about 40°

and 80°

C.

30. A method of forming an LED lamp with a desired distribution of phosphor, the method comprising:

selecting a desired position of phosphor particles with respect to an LED chip;

selecting a particle size of a plurality of phosphor particles based upon a temperature that correspondingly decreases a viscosity of an uncured polymer resin and based on the desired position of the phosphor particles with respect to the LED chip;

mixing the plurality of phosphor particles in the uncured polymer resin for which the viscosity can be controlled in response to temperature to form a substantially uniform suspension of the phosphor particles in the resin;

placing the uncured resin into a defined position adjacent the LED chip;

increasing the temperature of the resin in a first step to a temperature that correspondingly decreases the viscosity of the resin but that is less than the temperature at which the resin would cure unreasonably quickly;

encouraging the phosphor particles to settle in the lowered-viscosity resin to the desired position with respect to the LED chip for a period of at least about 10 minutes; and

in response to the phosphor particles having settled at the desired position, thereafter increasing the temperature of the substantially uncured resin to the point at which it will cure and solidify.

31. A method according to claim 30 comprising incorporating a polysiloxane resin.

32. A method according to claim 30 comprising incorporating a phosphor with a particle size that will remain suspended in the resin at temperatures of about 40°

C. or less, but that will settle within a reasonable period of time when the viscosity of the resin decreases.

33. A method of forming an LED lamp according to claim 30 wherein the step of mixing the phosphor particles comprises mixing particles of cerium doped yttrium aluminum garnet in the uncured polymer resin.

34. A method of forming an LED lamp according to claim 33 comprising mixing phosphor particles with an average particle size of about six microns.

35. A packaged light emitting diode formed by the method of claim 30.

36. A method according to claim 30, wherein increasing the temperature of the resin in the first step comprises increasing the temperature within a temperature range that has a maximum value of less than 100°

C.

37. A method according to claim 30, wherein selecting a particle size of the phosphor particles comprises selecting the particle size for controlling a migration of the phosphor particles during the first step.

38. A method according to claim 30, wherein increasing the temperature of the resin in the first step comprises increasing the temperature within a temperature range that has a maximum value of less than 100°

C. and a minimum value at room temperature.

39. A method according to claim 30, comprising selecting a time interval for permitting the phosphor particles to settle at the desired position, said time interval having a minimum value of about 10 minutes.

40. A method according to claim 39, wherein said time interval has a maximum value of about 5 hours.

41. A method of forming an LED lamp according to claim 30 comprising mixing the phosphor particles and the uncured polymer resin at a temperature of between about 25°

and 40°

C. prior to the step of placing the resin into the defined position adjacent the LED chip.

42. A method of forming an LED lamp according to claim 41 comprising the step of increasing the temperature fo the resin to between about 40°

and 80°

C. following the step of placing the uncured resin into the defined position.

43. A method of forming an LED lamp according to claim 30 wherein the step of increasing the temperature of the resin to the point at which it will cure comprises heating the resin to a temperature of between about 100°

and 200°

C.