Optoelectronic device encapsulant

• US 6,356,686 B1
• Filed: 09/03/1999
• Issued: 03/12/2002
• Est. Priority Date: 09/03/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kuczynski, Joseph Paul
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): Doan, Jennifer
• Application Number:
  US09/389,779
• Time in Patent Office: 921 Days
• Field of Search: 385/14, 385/49, 385/50, 385/52, 385/88, 385/89, 385/90, 385/92, 385/93, 385/39
• US Class Current: 385/39
• CPC Class Codes: G02B 6/421 the intermediate optical component consisting of a short length of fibre, e.g. fibre stub
• CPC Class Codes: G02B 6/4212 the intermediate optical element being a coupling medium interposed therebetween, e.g. epoxy resin, refractive index matching material, index grease, matching liquid or gel
• CPC Class Codes: G02B 6/4292 the light guide being disconnectable from the opto-electronic element, e.g. mutually self aligning arrangements

Abstract

An optically clear encapsulant for optoelectronic packages exhibits a suitably high viscosity both to replace a silicon nitride passivation layer required on a VCSEL die and to fill a gap between the die and an optical coupler, preventing light signal degradation. The encapsulant exhibits optical transparency to light having a wavelength of about 850 nanometers (nm) with substantially no Mie scattering since particulate fillers are not required to modulate viscosity in the encapsulant. Also, the encapsulant further seals wire bonds between the die and a cable header to prevent abrasive wear. The gap-filling encapsulant is particularly suitable for use with vertical cavity surface emitting laser (VCSEL) technology. The encapsulant includes prior to curing, a difunctional acrylate epoxy resin exhibiting pseudoplastic flow and a viscosity of greater than about 0.7×10⁶ centipoise. Accordingly, a method of manufacturing an optical subassembly may eliminate a separate passivation step and instead fill the gap between the die and optical coupler with an optically clear encapsulant.

Claims

1. An optoelectronic package comprising:

a) a substrate having an array of one or more sources or detectors, the sources or detectors adapted, respectively, to generate or receive a light signal;

b) an optical coupler aligned with the array such that a gap is formed between the optical coupler and the array of one or more sources or detectors, wherein the light signal passes through the gap between optical coupler and the array of one or more sources or detectors during operation; and

c) an optically transparent substrate encapsulant in contact with the substrate that substantially fills the gap between optical coupler and the array of one or more sources, wherein the encapsulant both passivates the sources or detectors and prevents interfering accumulations of matter from forming in the gap without degradation of the light signal, wherein the optically transparent comprises difunctional acrylated epoxy resin prior to curing.

2. The device of claim 1, wherein the encapsulant exhibits optical transparency to light having a wavelength of about 850 nanometers with substantially no Mie scattering.

3. The device of claim 1, wherein the sources comprise vertical cavity surface emitting lasers.

4. The device of claim 1, wherein the gap is greater than about 50 micrometers.

5. The device of claim 4, wherein the gap is about 100 micrometers.

6. The device of claim 1, further comprising wire bonds from the substrate to a cable header, wherein the encapsulant further seals the wire bonds from abrasive wear.

7. An encapsulant for an optoelectronic source comprising, prior to curing, a functionalized resin and an effective amount of a curing initiator, wherein the functionalized resin comprises difunctional acrylated epoxy resin, wherein, after curing, the encapsulant exhibits optical transparency to light having a wavelength of about 850 nanometers with substantially no Mie scattering and passivates the optoelectronic source.

8. The encapsulant of claim 7, wherein the encapsulant exhibits psuedoplastic flow prior to curing.

9. The encapsulant of claim 7, wherein the functionalized resin exhibits a viscosity of greater than about 0.7×

10⁶ centipoise prior to curing.

10. The encapsulant of claim 9, wherein the viscosity comprises about 1.2×

10⁶ centipoise.

11. The encapsulant of claim 7, wherein the initiator comprises a photo initiator.

12. The encapsulant of claim 7, wherein, after curing, the encapsulant exhibits thermal stability up to about 215°

C., adheres to gold or other metal layers suitable for tape automated bonding, and exhibits a moisture permeation rate of less than about 7 (gram×

milliinches)/(24 hours×

100 inches²).

13. A method of manufacturing an optical subassembly comprising the steps of:

affixing a non-passivated die to a die carrier, the die having an array of one or more sources or detectors, the sources or detectors adapted, respectively, to generate or receive a light signal;

aligning an optical coupler with the array such that a gap is formed between the optical coupler and the array of one or more sources or detectors, wherein the light signal passes through the gap between optical coupler and the array of one or more sources or detectors during operation;

dispensing an encapsulant on at least the array, wherein the encapsulant substantially fills the gap between the optical coupler and the array of one or more sources and prevents interfering accumulations of matter from forming in the gap, wherein the encapsulant comprises difunctional acrylated epoxy resin; and

curing the encapsulant, wherein the cured encapsulant exhibits optical transparency and passivates the sources or detectors.

14. The method of claim 13, wherein the cured encapsulant exhibits optical transparency to light having a wavelength of about 850 nanometers with substantially no Mie scattering.

15. The method of claim 13, wherein, prior to curing, the encapsulant comprises a functionalized resin, exhibiting a viscosity of greater than about 0.7×

10⁶ centipoise, and an effective amount of a curing initiator.

16. The method of claim 13, wherein the step of curing comprises exposing the encapsulant to ultraviolet radiation.

17. The method of claim 13, wherein the step of dispensing comprises further dispensing the encapsulant on wire bonds from the die to a cable header, wherein the encapsulant further seals the wire bonds from abrasive wear.

18. The method of claim 13, wherein the gap is greater than about 50 micrometers.

19. An optoelectronic package comprising:

a) a die having an array of one or more vertical cavity surface emitting lasers;

b) an optical coupler aligned with the array, wherein a gap is formed between the die and the optical coupler and wherein laser signals pass through the gap during operation;

c) an optically transparent substrate encapsulant in contact with the die, the encapsulant exhibiting substantially no Mie scattering and substantially filling the gap between the die and optical coupler, wherein the optically transparent substrate encapsulant comprises difunctional acrylated epoxy resin prior to curing; and

d) wire bonds from the die to a cable header, wherein the encapsulant both seals the lasers and wire bonds and prevents interfering accumulations of matter from forming in the gap.

20. An encapsulant for an optoelectronic source consisting essentially of, prior to curing, a difunctional acrylated epoxy resin and an effective amount of a curing photo initiator, wherein, prior to curing, the functionalized resin exhibits a viscosity of greater than about 0.7×

10⁶ centipoise and the encapsulant exhibits pseudoplastic flow and wherein, after curing, the encapsulant exhibits optical transparency to light having a wavelength of about 850 nanometers with substantially no Mie scattering and passivates the optoelectronic source.

21. A method of manufacturing an optical subassembly comprising the steps of:

affixing a non-passivated die to a die carrier, the die having an array of one or more vertical cavity surface emitting lasers;

forming wire bonds from the die to a cable header;

dispensing an encapsulant at least on the array and wire bonds, wherein the encapsulant comprises difunctional acrylated epoxy resin;

aligning an optical coupler with the array, wherein a gap is formed between the die and the optical coupler and wherein laser signals pass through the gap during operation;

curing the encapsulant by exposure to ultraviolet radiation, wherein the cured encapsulant exhibits optical transparency with substantially no Mie scattering, seals the lasers and wire bonds, substantially fills the gap between the die and optical coupler, and prevents interfering accumulations of matter from forming in the gap.