IMEC - INTECDepartment of Information Technologyhttp://www.intec.ugent.be

WAVEGUIDES IN BOARDS WAVEGUIDES IN BOARDS

BASED ONBASED ON ORMOCER ORMOCERs s geert.van.steenberge@intec.ugent.be

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OutlineOutline

Introduction ORMOCERs Laser ablation Waveguides Deflecting optics Coupling structure Conclusion

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IntroductionIntroduction

Integration of optical interconnects on board level Approaches

Fiber based Waveguide based

glass sheet polymers

http://www.circuitree.comPrinted Optical Waveguides: The Next Interconnect (H.Holden)

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ORMOCERORMOCERss

ORganic Modified CERamics Fraunhofer Institute - Germany Inorganic-Organic Hybrid Polymers Applications

microoptical elements (lenses, lens arrays, gratings, prisms) vertical integration: stacked optical waveguides (wafer scale) board level optical interconnects

General properties Compatibility with PCB manufacturing

lamination 180°C 200 Pascals assembly (solder reflow) up to 250°C

Good planarisation properties RMS roughness 2 - 4 nm Long-term stability under variable environmental conditions

(humidity, temperature) Low shrinkage

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ORMOCERORMOCERss

Optical properties (www.microresist.de)

Refractive index @ 830 nm (adjustable) CORE 1.5475 CLADDING 1.5306

Attenuation

Waveguides Photolithography Laser ablation

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ORMOCERORMOCERss

Application scheme

applicationspin-coating

softbake80-120 °C, <5 min

flood exposure

post exposure bake80-120 °C, <5 min

developmentcuring120-240 °C, up to 3 hrs

laser ablation

exposure

curing120-240 °C, up to 3 hrs

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Laser ablationLaser ablation Set-up

KrF Excimer Laser(can be tilted)248 nm

Frequency tripledNd-YAG Laser355 nm

CO2 Laser

9.6 m

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WaveguidesWaveguides UV-Defined

Cross section: 20 x 20 μm2 waveguides (250 μm pitch)

Laser-ablated Compatible with standard electrical PCB manufacturing (microvia’s) Adapt the pattern as a function of distortion in the substrate (FR4) Rapid prototyping Define microstructures and microoptics on a top surface of a

heterogeneous optoelectronic module in a very late phase of the assembly process

Entire optical interconnection using one technology

OPTICAL LAYERS

COPPER

FR4

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WaveguidesWaveguides Laser-ablated

Laser beam moves over surface Technology sequence

bottom cladding layer core layer laser ablation microstructuring upper cladding layer

Experimental results KrF Excimer laser (248 nm)

50 x 50 μm2

trapezoidal shape low ablation speed roughness to high

1st ablation

2nd ablation

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WaveguidesWaveguides Frequency tripled Nd-YAG laser (355 nm)

50 x 50 μm2

clean surfaces ablation speed: 1 mm/s

photo-dissociation photo-thermal ablation

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Deflecting opticsDeflecting optics

45 micromirrors micro machining techniques (90 V-shaped diamond blade)

excellent cut surface difficult to cut individual waveguides on the same substrate

(physical size of the machining tool)

remove waveguide film from substrate

cutting from back-side

diamond blade

claddingcorecladding

substrate

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Deflecting opticsDeflecting optics 45 micromirrors

reactive ion etching RIE (45 oblique etching) limited by directional freedom different process steps

temperature controlled RIE (90 RIE + heat treatment) not limited by directional freedom material dependent

laser ablation set-up: excimer laser beam can be tilted

– Total Internal Reflection (TIR) negative facet

– coated mirror (Al, Au)positive facet

RIE

Al maskcladdingcorecladding

substrate

TIR condition crucial glue (mounting lens plate) humidity

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Deflecting opticsDeflecting optics Total Internal Reflection

Smooth surface Tapering compensated Flatness of the mirror at core layer

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Coupling structureCoupling structure Example: MT-compatible coupling

Microlenses and 700 m holes ablated in a polycarbonate (PC) plate (Kris Naessens, Ph.D. thesis Ghent University)

Alignment: ribbon - lenses: 700 m pins match holes in PC plate

Alignment: micromirror - lenses: flip chip set-up (alignment marks)

Lenses ablated in upper-cladding layer Visual alignment under ablation set-up

with respect to 45 micromirror

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ConclusionConclusion

Integration of optical interconnects on board level polymer waveguides

Compatibility with the manufacturing and assembly processes of the conventional electrical board technology ORMOCERs Laser ablation

Entire optical interconnection using one technology Waveguides Micromirrors Microlenses Alignment features

SEM pictures show very smooth surfaces