LED bonding structures and methods of fabricating LED bonding structures

• US 20050253154A1
• Filed: 04/26/2005
• Published: 11/17/2005
• Est. Priority Date: 04/28/2004
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Edmond, John Adam, Slater, David Beardsley Jr.
• Granted Patent: US 7,462,861 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• CPC Class Codes: H01L 2224/32245 the item being metallic
• CPC Class Codes: H01L 2224/48463 the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• 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 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/12032 Schottky diode
• CPC Class Codes: H01L 2924/12041 LED
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/40 Materials therefor
• 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

Abstract

An LED chip includes a bond pad suitable for thermosonic or thermocompression bonding such as Sn, AuSn or other metals. The physical dimensions of the bond pad are selected to discourage or prevent solder squeeze-out during thermocompression or thermosonic bonding with or without flux. In some embodiments, an AuSn bond pad is designed to accept 30 g to 70 g of force or more without squeeze-out.

Claims

1. An LED chip comprising:

an epitaxial region comprising at least a p-type layer and an n-type layer;

an ohmic contact formed on at least one of the p-type layer or the n-type layer; and

a bond pad formed on the ohmic contact, the bond pad having a total volume less than about 3×

10<sup>−

5</sup> mm³.

2. An LED chip as recited in claim 1, wherein the bond pad comprises a metal solder.

3. An LED chip as recited in claim 1, wherein the bond pad comprises Au, Au/Sn, Pb/Sn, Sn or Sn/Ag.

4. An LED chip as recited in claim 1, wherein the bond pad has a total volume less than about 2.5×

10<sup>−

5</sup> mm³.

5. An LED chip as recited in claim 1, wherein the bond pad is formed in the shape of a parallelepiped having a generally square periphery.

6. An LED chip as recited in claim 5, wherein the epitaxial region has a width of about 250 μ

m or more, and wherein the bond pad has a height of about 1.2 μ

m or less and a width of about 150 μ

m or less.

7. An LED chip as recited in claim 1, wherein the bond pad is formed in the shape of a cylinder.

8. An LED chip as recited in claim 7, wherein the epitaxial region has a width of about 250 μ

m or more, and wherein the bond pad has a height of about 2 μ

m or less and a diameter less than one half the width of the epitaxial region.

9. An LED chip as recited in claim 8, wherein the bond pad has a diameter of about 120 μ

m or less.

10. An LED chip as recited in claim 1, wherein the bond pad is formed in the shape of a polyhedron having opposing parallel faces and a star-shaped periphery.

11. An LED chip as recited in claim 10, wherein the distance from an edge of the bond pad to an edge of the epitaxial region is at least about 50 μ

m.

12. An LED comprising:

an LED chip having an epitaxial region comprising at least a p-type layer and an n-type layer, an ohmic contact formed on at least one of the p-type layer or the n-type layer, and a bond pad formed on the ohmic contact, the bond pad having a total volume less than about 3×

10<sup>−

5</sup> mm³;

wherein the LED chip is bonded via the bond pad onto a submount,

and wherein a shear strength of the bond between the LED chip and the submount exceeds 140 g.

13. An LED as recited in claim 12, wherein the epitaxial region comprises a perimeter and the bond pad comprises a metal solder that is located entirely within the perimeter of the epitaxial region.

14. An LED as recited in claim 12, wherein the total volume of the bond pad is less than the space volume between the ohmic contact layer and the submount.

27. An LED as recited in claim 12, wherein the shear strength of the bond between the LED chip and the submount exceeds 300 g.

15. A method of fabricating an LED comprising:

providing an LED chip having an epitaxial region comprising at least a p-type layer and an n-type layer, an ohmic contact formed on at least one of the p-type layer or the n-type layer, and a bond pad formed on the ohmic contact, the bond pad having a total volume less than about 3×

10<sup>−

5</sup> mm³;

bonding the LED chip to a submount via thermocompression or thermosonic bonding.

16. A method as recited in claim 15, wherein the step of bonding the LED chip to a submount comprises applying a force of about 30 to 70 g to the LED chip.

17. A method as recited in claim 16, wherein the applied force is about 50 g.

18. A method as recited in claim 15, wherein the LED chip includes a substrate, and the ohmic contact is formed on a surface of the epitaxial region opposite the substrate.

19. A method as recited in claim 15, wherein the bond pad has a total volume less than about 2.5×

10<sup>−

5</sup> mm³.

20. A method as recited in claim 15, wherein the bond pad is formed in the shape of a parallelepiped having a generally square periphery.

21. A method as recited in claim 20, wherein the epitaxial region has a width of about 250 μ

m or more, and wherein the bond pad has a height of about 1.2 μ

m or less and a width of about 150 μ

m or less.

22. A method as recited in claim 15, wherein the bond pad is formed in the shape of a cylinder having a generally circular periphery.

23. A method as recited in claim 22, wherein the epitaxial region has a width of about 250 μ

m or more, and wherein the bond pad has a height of about 2 μ

m or less and a diameter less than one half the width of the epitaxial region.

24. A method as recited in claim 23, wherein the bond pad has a diameter of about 120 μ

m or less.

25. A method as recited in claim 15, wherein the bond pad is formed in the shape of a polyhedron having opposing parallel faces and a star-shaped or cross-shaped periphery.

26. A method as recited in claim 25, wherein the distance from an edge of the bond pad to an edge of the epitaxial region is at least about 20 μ

m.