System and method for enhanced LED thermal conductivity

• US 6,921,927 B2
• Filed: 08/28/2003
• Issued: 07/26/2005
• Est. Priority Date: 08/28/2003
• Status: Expired due to Term

• Current Assignee: Document Security Systems, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Ng, Kee Yean, Yoganandan, Sundar A. L. N.
• Primary Examiner(s): JACKSON JR, JEROME
• Application Number:
  US10/650,892
• Publication Number:
  US 20050045902A1
• Time in Patent Office: 698 Days
• Field of Search: 257/99, 257/100, 257/707, 257/745, 257/459
• US Class Current: 257/99
• CPC Class Codes: H01L 2224/32245 the item being metallic
• CPC Class Codes: H01L 2224/32257 the layer connector connecting to a bonding area disposed in a recess of the surface of the item
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 24/73 Means for bonding being of different types provided for in two or more of groups H01L24/10, H01L24/18, H01L24/26, H01L24/34, H01L24/42, H01L24/50, H01L24/63, H01L24/71
• 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 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• 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 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/12041 LED
• CPC Class Codes: H01L 33/56 Materials, e.g. epoxy or silicone resin
• 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 33/641 characterized by the materials
• CPC Class Codes: H01L 33/642 characterized by the shape
• CPC Class Codes: H01L 33/647 the elements conducting electric current to or from the semiconductor body

Abstract

A light emitting device assembly comprises a light emitting diode (LED) chip, a substrate with two terminals, at least one encapsulation layer, and a thermally conductive adhesive to connect the LED chip and the substrate. The first terminal of the substrate is comprised of a portion with a width at least as wide as the LED chip and a vertical cross-sectional area of at least 30% of the total vertical cross-sectional area of the encapsulated assembly, and a straight element. The enlarged first terminal portion provides more area for heat dissipation and conduction, and along with the thermally conductive adhesive and the encapsulation package, provide enhanced thermal conductivity.

Claims

1. A light emitting device assembly comprising:

at least one encapsulation layer encasing

(a) a light emitting diode (LED) chip,

(b) a substrate having two terminals, a first one of said two terminals having an electrical lead and a portion with a width at least as wide as said LED chip and a vertical cross-sectional area of at least 30% of the total vertical cross-sectional area of said encased assembly wherein said LED chip is located on an edge of said first terminal opposite said electrical lead, and

(c) an adhesive that connects said LED chip to said first terminal of said substrate.

2. The light emitting device assembly of claim 1 wherein said adhesive is thermally conductive.

3. The light emitting device assembly of claim 1 wherein said adhesive is metal-based.

4. The light emitting device assembly of claim 1 wherein said portion of said first terminal is enlarged so as to protrude from said at least one encapsulation layer.

5. The light emitting device assembly of claim 4 wherein said portion of said first terminal is placed in contact with another metal surface so as to further increase thermal conductivity.

6. The light emitting device assembly of claim 1 wherein said portion of said first terminal is enlarged so as to be at least flush with an edge of said at least one encapsulation layer.

7. The light emitting device assembly of claim 1 wherein said portion of said first terminal has increased thickness to increase thermal capacity of said assembly and to sink more heat from said LED chip.

8. The light emitting device assembly of claim 1 wherein said at least one encapsulation layer is comprised of:

a first layer encapsulant with enhanced thermal conducting properties wherein said first layer encapsulant substantially encases said portion of said first terminal; and

a second layer encapsulant which is attached to said first layer encapsulant on one side to encapsulate the remainder of said assembly.

9. The light emitting device assembly of claim 8 wherein said second layer encapsulant is optically clear.

10. The light emitting device assembly of claim 8 wherein said first layer encapsulant is selected from the group consisting of:

transparent material;

semi-transparent material;

opaque material; and

polymer-based material.

11. The light emitting device assembly of claim 8 wherein said first layer encapsulant is comprised of fillers to enhance thermal conductivity.

12. The light emitting device assembly of claim 11 wherein said fillers are ceramic, glass or aluminum particles.

13. The light emitting device assembly of claim 1 wherein said adhesive is selected from a group comprised of at least:

a solder alloy;

a tin-based or gold-based alloy; and

indium.

14. The light emitting device assembly of claim 1 wherein said vertical cross-sectional area of said portion of said first terminal is at least 0.014 in².

15. The light emitting device assembly of claim 14 wherein said at least one encapsulant layer encapsulates a 5 mm through-hole lamp.

16. A system comprising:

at least one encapsulation layer encasing an assembly, wherein said assembly includes

(a) at least one light emitting diode (LED) chip;

(b) a first terminal, said first terminal entering said encapsulation layer through an edge and wherein said first terminal has an electrical lead and a portion with a width at least as wide as said LED chip wherein said portion of said first terminal extends so as to be at least flush with said edge of said at least one encapsulation layer and wherein said portion is disposed between said LED chip and said electrical lead;

(c) at least one second terminal, wherein the number of said at least one second terminal corresponds to the number of said at least one LED chip; and

(d) at least one adhesive connecting said at least one LED chip to said first terminal.

17. The system of claim 16 wherein said at least one encapsulation layer is comprised of:

a first layer encapsulant with enhanced thermal conducting properties wherein said first layer encapsulant substantially encases said portion of said first terminal; and

a second layer encapsulant which is attached to said first layer encapsulant on one side to encapsulate the remainder of said assembly.

18. The system of claim 16 wherein said assembly has a thermal resistance of at most 150°

C/W.