Light emitting devices with a phosphor coating having evenly dispersed phosphor particles and constant thickness

• US 7,129,638 B2
• Filed: 08/08/2001
• Issued: 10/31/2006
• Est. Priority Date: 08/09/2000
• Status: Expired due to Term

• Current Assignee: Document Security Systems, Inc.
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Ng, Ke Yean
• Primary Examiner(s): Santiago, Mariceli
• Application Number:
  US09/924,653
• Publication Number:
  US 20020021085A1
• Time in Patent Office: 1,910 Days
• Field of Search: 313/499, 313/512, 313/498, 313/501, 313/502, 313/113, 313/506, 313/485, 315/169.3, 257/99, 257/98, 257/100
• US Class Current: 313/512
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48257 connecting the wire to a die pad of the item
• 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 2224/8592 Applying permanent coating, e.g. protective coating
• 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 2933/0041 relating to wavelength conversion elements
• CPC Class Codes: H01L 33/486 adapted for surface mounting
• CPC Class Codes: H01L 33/505 characterised by the shape, e.g. plate or foil

Abstract

A light emitter, being an LED or laser diode, is disposed above a base substrate, and a coating material containing a dye compound, such as an epoxy material containing a fluorescent or luminescent substance, is applied over the light emitter. The base substrate includes a raised platform on which the light emitter is mounted, such that the light emitter is supported at a prescribed distance from the surrounding base substrate. The device allows the dye compound within the coating material to settle into the recessed base substrate surrounding the platform and leave the sides of the light emitter able to retain only a coating of the dye comparable in thickness to that coating remaining on the upper surface of the light emitter, in order to improve the uniformity of the light distribution pattern emitted from the device.

Claims

1. A light emitting device, comprising:

a base substrate with a cavity and a trough to form a reflective cup;

a projecting platform at the base of the cavity, the projecting platform having vertical walls;

a light emitter mounted on the projecting platform, the light emitter being smaller in outline than the projecting platform; and

a coating having an adhesive material and particles of another substance, wherein the coating is a viscous slurry when applied over and in direct contact with the light emitter in the cavity, and hardens when cured after being applied over the light emitter in the cavity, wherein when the coating, when being a viscous slurry, is applied over the light emitter, the platform, the cavity, and the trough allow the particles in the coating to be evenly settled on and around the light emitter within the cavity before the coating is cured, resulting in an evenly dispersed, uniform thickness particle coating over the light emitter, the thickness of the particle coating being constant with respect to the light emitter.

2. The device according to claim 1, wherein the platform is formed as an integral part of the base substrate.

3. The device according to claim 1, wherein the platform is a discrete component attachable to the base substrate.

4. The device according to claim 3, wherein the platform and the base substrate are fabricated from different materials.

5. The device according to claim 4, wherein the base substrate comprises a metal and the platform comprises a material able to efficiently dissipate heat generated by the light emitter.

6. The device according to claim 1, wherein the reflective cup provides reflection of light emitted by the light emitter.

7. The device according to claim 6, wherein the cavity has a sloping wall which is of frusto-conical form surrounding the projecting platform, and the sloping wall and the platform are coated with a reflective material.

8. The device according to claim 1, wherein the reflective material is silver.

9. The device according to claim 1, wherein the platform allows the particles within the coating to settle to a lower position with respect to the light emitter towards the periphery of the base of the cavity before the coating is cured, thus allowing the thickness of the coating that contains the settled particles to remain constant over the entire surface and sides of the light emitter.

10. The device according to claim 1, wherein the particles are of fluorescent or luminescent substance to absorb light of one wavelength and re-emit light of a different wavelength.

11. The device according to claim 10, wherein the fluorescent or luminescent substance is phosphor and the adhesive material is epoxy.

12. The device according to claim 1, further comprising a lens positioned over the light emitter and the coating material to focus the emitted light from the light emitter.

13. The device according to claim 1, wherein the light emitter is selected from the group of an LED and a laser diode.