Surface mountable light emitting device

• US 6,803,607 B1
• Filed: 06/13/2003
• Issued: 10/12/2004
• Est. Priority Date: 06/13/2003
• Status: Active Grant

• Current Assignee: Huizhou Light Engine Limited
• Original Assignee: Cotco Holdings Limited
• Inventors: Lau, Victor Yue Kwong, Chan, Keong Mun
• Primary Examiner(s): Cao, Phat X.
• Application Number:
  US10/462,089
• Time in Patent Office: 487 Days
• Field of Search: 257/98, 257/100, 257/95, 257/79
• US Class Current: 257/98
• CPC Class Codes: F21K 9/232 specially adapted for generating an essentially omnidirectional light distribution, e.g. with a glass bulb
• CPC Class Codes: F21K 9/61 using light guides
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48095 Kinked
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• 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 2924/1815 Shape
• CPC Class Codes: H01L 33/486 adapted for surface mounting
• CPC Class Codes: H01L 33/54 having a particular shape

Abstract

This invention relates to a surface mountable light emitting device in which the lead frame is exposed over a substantial portion of the underside of the device so as to allow greater thermal conductivity to any device on which it may be mounted. The LED provides the lens and a molded body to encapsulate the lead frame and an electrical contact in a single molding step while the lead frames and further contacts are arranged in a suitable array. The lens couples the luminous output of a light-emitting diode (LED) to a predominantly spherical pattern comprises a transfer section that receives the LED'"'"'s light within it and an ejector atop it that receives light from the transfer section and spreads it spherically. Applications may include, but are not limited to, household light bulbs and car headlights.

Claims

1. A high power surface mountable light emitting device comprising:

a light emitting semiconductor chip;

a thermally and electrically conductive lead frame connected to said chip and exposed over a substantial portion of the underside of the device;

a lead wire from said chip to a contact exposed at least partially on a side of said device; and

a lens over said chip wherein the lens comprises;

a lower transfer section; and

an upper ejector section situated upon the lower transfer section, said lower transfer section operable for placement upon the light emitting semiconductor chip and operable to transfer the radiant emission to said upper ejector section, said upper ejector section shaped such that the emission is redistributed externally into a substantial solid angle.

2. The device of claim 1 wherein the lower transfer section is a solid of revolution having a profile in the shape of an ellipse with a long axis parallel to an axis of revolution of the solid and displaced laterally therefrom so as to place the focus of said elliptical profile on the opposite side of said axis.

3. The device of claim 2 wherein the upper ejector section is a cylinder of the same diameter as a top diameter of the transfer section, said cylinder having a conical depression on its top surface.

4. The device of claim 2 wherein said lateral displacement substantially equals the radius of said ellipsoid at its focus.

5. The device of claim 1 wherein said upper ejector section is a conicoid.

6. The device of claim 1 wherein said upper ejector section is a everted sphere.

7. The device of claim 1 wherein said upper ejector section is an indented section of a sphere.

8. The device of claim 4 wherein said upper ejector section is a cylinder.

9. The device of claim 1 wherein the upper ejector section has a diffusive surface.

10. The device of claim 1 wherein the lens has a surface with graded sub-wavelength roughness for reflective scattering of said emitted light out of said device.

11. The device of claim 1 wherein the lens is made of transparent material for distributing the radiant emission of a light emitter, comprising an expander section for receiving said radiant emission and narrowing its angular range to that of light guiding via total internal reflection, and a cylindrical ejector section for receiving said angularly narrowed radiation and ejecting it by means of graded sub-wavelength roughness on its surface.

12. The device of claim 1 wherein said lens comprises substantially encasement of an upper side of said chip in a transparent compound.

13. The device of claim 12 wherein said transparent compound forms both a lens and a portion of the body about the lead frame.

14. The device of claim 13 wherein said transparent compound is keyed into the metallic lead frame and said contact to reduce separation.

15. The device of claim 1 wherein said device includes a reflector cup about said chip to reflect light from the sides of the chip generally into a direction extending from the upper surface of said chip.

16. The device of claim 15 wherein said reflector cup is metallic.

17. The device of claim 15 wherein said reflector cup comprises a core material with a highly reflective metallic coating.

18. The device of claim 17 wherein said reflective coating comprises chromium or silver plating.

19. The device of claim 18 wherein said lead frame comprises a substantially copper core with at least one other metal plating on an underside thereof.

20. The device of claim 19 wherein said metal plating on said underside of said lead frame comprises a plating of solder of palladium.

21. The device of claim 15 wherein said transparent compound comprises an epoxy resin.

22. The device of claim 1 wherein said lead wire to said contact is a gold wire.