Light emitting diode for harsh environments

• US 8,415,184 B2
• Filed: 05/09/2011
• Issued: 04/09/2013
• Est. Priority Date: 03/08/2007
• Status: Active Grant

• Current Assignee: Senseonics, Incorporated (Senseonics Holdings, Inc.)
• Original Assignee: Sensors For Medicine and Science Incorporated
• Inventors: Colvin, Jason D., Colvin, Arthur E. Jr., DeHennis, Andrew, Krsmanovic, Jody L.
• Primary Examiner(s): Valentine, Jami M
• Application Number:
  US13/103,561
• Publication Number:
  US 20120034717A1
• Time in Patent Office: 701 Days
• Field of Search: 257/79, 257/98, 257/99, 257/E33.056, 257/E33.067, 438/27, 356/442
• US Class Current: 438/27
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: G01N 21/6428 Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" in vivo A61B5/00; immunoassay G01N33/53
• CPC Class Codes: G01N 21/8507 Probe photometers, i.e. with optical measuring part dipped into fluid sample
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48472 the other connecting portion not on the bonding area also being a wedge bond, i.e. wedge-to-wedge
• CPC Class Codes: H01L 25/167 comprising optoelectronic devices, e.g. LED, photodiodes
• 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 2924/01087 Francium [Fr]
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 31/0203 Containers; Encapsulations , e.g. encapsulation of photodiodesfor photovoltaic devices H01L31/048; for organic photosensitive devices H10K30/80
• CPC Class Codes: H01L 31/125 Composite devices with photosensitive elements and electroluminescent elements within one single body
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/483 : Containers
• CPC Class Codes: H01L 33/52 : Encapsulations
• CPC Class Codes: H01L 33/54 : having a particular shape
• 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

A light emitting diode for harsh environments includes a substantially transparent substrate, a semiconductor layer deposited on a bottom surface of the substrate, several bonding pads, coupled to the semiconductor layer, formed on the bottom surface of the substrate, and a micro post, formed on each bonding pad, for electrically connecting the light emitting diode to a printed circuit board. An underfill layer may be provided between the bottom surface of the substrate and the top surface of the printed circuit board, to reduce water infiltration under the light emitting diode substrate. Additionally, a diffuser may be mounted to a top surface of the light emitting diode substrate to diffuse the light emitted through the top surface.

Claims

1. A method for mounting a light emitting diode to a printed circuit board in a flip chip orientation, comprising:

removing a reflective layer from a first surface of the light emitting diode;

bonding micro posts to bonding pads on a second surface of the light emitting diode, the second surface being opposite the first surface;

bonding the micro posts to corresponding bonding pads on the printed circuit board so that the light emitting diode is mounted in a flip chip orientation; and

mounting a diffuser on the first surface of the light emitting diode to diffuse the light emitted through the first surface of the light emitting diode.

2. The method of claim 1, wherein the light emitting diode comprises a substantially transparent substrate.

3. The method of claim 2, wherein the substrate is sapphire.

4. The method of claim 1, wherein the light emitting diode comprises a semiconductor layer.

5. The method of claim 4, wherein the semiconductor layer includes at least one p-n junction.

6. The method of claim 1, wherein the bonding pads on the second surface of the light emitting diode, the bonding pads on the printed circuit board and the micro posts are gold.

7. The method of claim 1, wherein the micro posts are bonded to the bonding pads on the second surface of the light emitting diode and to the bonding pads on the printed circuit board using thermocompression bonding, thermosonic bonding, ultrasonic bonding, or welding.

8. The method of claim 1, further comprising forming an underfill layer, including a polymer and a filler, between the second surface of the light emitting diode and a first surface of the printed circuit board, to reduce water infiltration between the light emitting diode and the printed circuit board.

9. The method of claim 8, wherein the polymer is cyanate ester.

10. The method of claim 8, wherein the filler includes a plurality of microballoons, and each microballoon of the plurality of microballoons has a diameter from 2 μ

m to 11 μ

m.

11. The method of claim 9, wherein the filler includes a plurality of microballoons, and each microballoon of the plurality of microballoons is a gas-filled sphere having a diameter of 11 μ

m and a wall thickness of 1 μ

m.

12. The method of claim 9, wherein the filler includes a plurality of microballoons, and the microballoons are pre-treated with an adhesion promoter.

13. The method of claim 12, wherein the adhesion promoter is silane.

14. The method of claim 8, wherein the filler is a light-scattering filler and the polymer is an optical epoxy.

15. The method of claim 14, wherein the light-scattering filler is titanium oxide and the optical epoxy is Epo-Tek 301-2.

16. The method of claim 8, wherein the underfill layer is 70% by weight of polymer and 30% by weight of filler.

17. The method of claim 1, wherein the diffuser includes titanium oxide to increase light reflectivity.

18. The method of claim 1, wherein the diffuser includes microballoons to increase light reflectivity.

19. The method of claim 1, the diffuser is a substantially transparent, hemispherical diffuser.

20. A method for mounting a light emitting diode to a printed circuit board in a flip chip orientation, comprising:

bonding first and second micro posts to first and second bonding pads, respectively, on a surface of the light emitting diode;

bonding the first and second micro posts to corresponding bonding pads on the printed circuit board so that the light emitting diode is mounted in a flip chip orientation;

forming an underfill layer, including a polymer and a filler, between the surface of the light emitting diode and a first surface of the printed circuit board, to reduce water infiltration between the light emitting diode and the printed circuit board;

wherein the filler includes a plurality of microballoons.

21. The method of claim 20, wherein the light emitting diode comprises a substantially transparent substrate.

22. The method of claim 21, wherein the substrate is sapphire.

23. The method of claim 20, wherein the light emitting diode comprises a semiconductor layer.

24. The method of claim 23, wherein the semiconductor layer includes at least one p-n junction.

25. The method of claim 20, wherein the first and second bonding pads on the surface of the light emitting diode, the bonding pads on the printed circuit board and the first and second micro posts are gold.

26. The method of claim 20, wherein the first and second micro posts are bonded to the first and second bonding pads on the surface of the light emitting diode and to the bonding pads on the printed circuit board using thermocompression bonding, thermosonic bonding, ultrasonic bonding, or welding.

27. The method of claim 20, wherein each microballoon of the plurality of microballoons has a diameter from 2 μ

m to 11 μ

m.

28. The method of claim 20, wherein each microballoon of the plurality of microballoons is a gas-filled sphere having a diameter of 11 μ

m and a wall thickness of 1 μ

m.

29. The method of claim 20, wherein the microballoons are pre-treated with an adhesion promoter.

30. The method of claim 29, wherein the adhesion promoter is silane.

31. The method of claim 20, wherein the filler is a light-scattering filler and the polymer is an optical epoxy.

32. The method of claim 31, wherein the light-scattering filler is titanium oxide and the optical epoxy is Epo-Tek 301-2.

33. The method of claim 20, wherein the underfill layer is 70% by weight of polymer and 30% by weight of filler.

34. The method of claim 20, wherein the surface of the light emitting diode is a second surface of the light emitting diode, and the method further comprises removing a reflective layer from a first surface of the light emitting diode, the first surface of the light emitting diode being opposite the second surface of the light emitting diode.

35. The method of claim 34, further comprising mounting a diffuser on the first surface of the light emitting diode to diffuse the light emitted through the first surface of the light emitting diode.

36. The method of claim 35, wherein the diffuser includes titanium oxide to increase light reflectivity.

37. The method of claim 35, wherein the diffuser includes microballoons to increase light reflectivity.

38. The method of claim 35, wherein the diffuser is a substantially transparent, hemispherical diffuser.

39. The method of claim 20, wherein the polymer is cyanate ester.