Stenciling phosphor layers on light emitting diodes

• US 20040097006A1
• Filed: 11/06/2003
• Published: 05/20/2004
• Est. Priority Date: 10/13/2000
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Lowery, Christopher H.
• Granted Patent: US 7,049,159 B2
• Time in Patent Office: Days
• US Class Current: 438/99
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil

Abstract

A method for forming a luminescent layer on a light emitting semiconductor device includes positioning a stencil on a substrate such that a light emitting semiconductor device disposed on the substrate is located within an opening in the stencil, depositing a stenciling composition including luminescent material in the opening, removing the stencil from the substrate, and curing the stenciling composition to a solid state. The resulting light emitting device includes a stack of layers including semiconductor layers comprising an active region and a luminescent material containing layer having a substantially uniform thickness disposed around at least a portion of the stack. A surface of the luminescent material containing layer not adjacent to the stack substantially conforms to a shape of the stack. In one embodiment, the light emitting device emits white light in a uniformly white spatial profile.

Claims

1. A method for forming a luminescent layer on a light emitting semiconductor device, the method comprising:

positioning a stencil on a substrate such that a light emitting semiconductor device disposed on said substrate is located within an opening in said stencil;

depositing a stenciling composition including luminescent material in said opening;

removing said stencil from said substrate; and

curing said stenciling composition to a solid state.

2. The method of claim 1, wherein said opening substantially conforms to a shape of said light emitting semiconductor device.

3. The method of claim 1, wherein a depth of said opening is about equal to a sum of a height of said light emitting semiconductor device and a thickness of said luminescent layer.

4. The method of claim 1, wherein a width of said opening is about equal to a sum of a width of said light emitting semiconductor device and twice a thickness of said luminescent layer.

5. The method of claim 1, wherein said stenciling composition comprises fumed silica particles and at least one silicone polymer.

6. The method of claim 5, wherein said fumed silica particles have a ratio of surface area per unit mass greater than about 90 m²/g.

7. The method of claim 1, wherein said silicone polymer has a viscosity of about 1,000 centistokes to about 20,000 centistokes.

8. The method of claim 1, further comprising:

positioning said stencil such that each one of a plurality of light emitting semiconductor devices disposed on the substrate is located within a corresponding one of a plurality of openings in the stencil; and

depositing the stenciling composition in each of said openings.

9. A luminescent stenciling composition comprising:

an optically clear silicone polymer;

phosphor particles; and

silica particles;

wherein said phosphor particles and said silica particles are dispersed in said silicone polymer.

10. The luminescent stenciling composition of claim 9, wherein said silicone polymer has a viscosity of about 1,000 centistokes to about 20,000 centistokes.

11. The luminescent stenciling composition of claim 9, wherein a concentration by weight of said phosphor particles is about 1:

5 to about 1;

0.8 with respect to said silicone polymer.

12. The luminescent stenciling composition of claim 9, wherein said phosphor particles comprise yttrium aluminum garnet doped with gadolinium and cerium.

13. The luminescent stenciling composition of claim 9, wherein said silica particles are fumed silica particles.

14. The luminescent stenciling composition of claim 13, wherein said fumed silica particles have a ratio of surface area per unit mass greater than about 90 m²/g.

15. The luminescent stenciling composition of claim 9, wherein a concentration by weight of said fumed silica particles is about 1:

70 to about 1;

20 with respect to said silicone polymer.