Laser Ablation of Polymer Waveguide and Integrated Mirrors for Optical Circuit Boards

Laser Ablation of Multimode Polymer

Waveguide and Integrated Mirrors for Optical

Circuit Boards

© Shefiu S. Zakariyah

[email protected]

Shefiu S. Zakariyah

Presentation Overview

Introduction

Optical communication overview

IeMRC OPCB flagship project

Laser ablation of optical waveguides

Results

o System characterisation

o Waveguides

Challenges

Summary

Optical Communication System

VCSEL / LED Air / glass /

polymer Photodiode

Core

Cladding

Blo

ck /

Mo

du

le

Prin

cip

le

Ele

men

t /

Co

mp

on

en

t

Transmitter Information

Channel Receiver

Optical Communication Methods

Optical Communication

Long-distance

Guided (e.g. optical fiber)

Unguided (e.g. free space)

Short-distance

Guided (e.g. OPCB)

Unguided (e.g. free space)

OPCB (Optical Printed Circuit Board) is the integration of optical waveguides with PCB to

solve the bottlenecks on the current electrical connections.

Current Challenges in PCBs for HDI

Copper Interconnection Limitation

Copper transmission reaches limits.

HDI cannot absolutely solve the density challenges in PCB industry.

EMI, crosstalk, reflection, etc. at high frequency.

Optical Interconnection Benefits

High data rate and information capacity.

Reduced power consumption.

Relative cost effectiveness.

Small size (reduced space).

No EMI issue.

Optical

Interconnection

Electrical

Interconnection

6.25 Gb/s cross-over point

Bandwidth

Co

st

Exxelis (Polymer Supply and

Photolithography)

UCL (Waveguide Design Rules

and Optical Modelling &

Measurement)

Heriot-Wattt University (Polymer Formulation and

Laser Direct Writing of

Waveguides)

Dow Corning (Polymer Supply and

Photolithography)

Cadence (PCB Design Tools and

Rules)

NPL (Physical Measurements)

Stevenage Circuits Ltd (PCB Samples, Dry Films,

CAD Conversion and Laser

Ablation)

Loughborough

University (laser Ablation and Ink-jet

Printing of Waveguides)

BAE Systems

(In-flight Interconnect)

Renishaw

(Precision

Measurement)

Xyratex (Network Storage

Interconnect)

End Users

IeMRC OPCB Flagship Collaboration

Project Aims:

Establishing waveguide design rules.

Developing low cost manufacturing

techniques.

Understanding the effects of

waveguide wall roughness.

cross sectional shape.

on the behaviour of light and the effect

on waveguide loss.

Academic partners: Loughborough

University, Heriot-Watt University and

University College London.

Industrial partners: Xyratex,

Stevenage Circuits, Renishaw, BAE

Systems, Exxelis, Dow Corning, Cadence

and NPL.

Optical Waveguide Fabrication Techniques

Photolithography

Laser direct writing

Inkjet-printing

Laser ablation

Photochemical (UV sources, e.g. Excimer)

Photothermal (IR sources, e.g. CO2)

Laser Material Processing

Laser Material Processing

Laser Generation Beam Delivery System Laser Processing (Material & Workpiece)

Laser Beam Monitoring

Laser Ablation of Polymer Waveguides

Stage1 : Spin coating of clad and core layers which

are UV-cured individually.

Stage2 : Laser ablation of optical layer from the

core through to the clad layer

Stage3 : Deposition of upper cladding

FR4 substrate

Lower clad

Core

PitchClad material

Core

FR4 substrate

FR4 substrate

Research Processes and Procedures

Materials

Truemode-polyacrylate

(supplied by Exxelis).

OE4140 / OE4141

polysiloxane (supplied by

Dow Corning).

Both UV cure photopolymers.

Lasers

10.6 µm CO2

355 nm UV Nd:YAG

248 nm Excimer

Laser ablated channel (1)




20

0 µ

m

50 µm

Waveguide (1)

Waveguide (2)

Waveguide (3)

Laser Ablation of Polymer Waveguides

248 nm Excimer

Laser system characterisation

Fabrication of waveguides Mirror design & fabrication

for in-plane coupling

Laser System & Experimental Investigation

355 nm UV Nd:YAG

Feasibility study of optical polymer machining


Fabrication of waveguides

248 nm Excimer





10.6 µm CO2


Laser micromachining Fabrication of waveguides

355 nm UV Nd:YAG



Fabrication of waveguides

248 nm Excimer





Incre

ase in

pro

cessin

g s

peed

Incre

ase in s

yste

m c

apabili

ties

Line ablated using the Gaussian beam

profile CO2 laser.

CO2 Laser Ablation of Optical Waveguides

CO2 Laser System 10 Watt (max.) power

Wavelength = 10.6 m

Continuous Wave (CW)

Gaussian beam profile

Investigation Photothermally-dominated ablation

process.

Feasibility study was conducted.

Effect of translation speed & power was investigated.

Material Polysiloxane OE4140 / OE4141

(Dow Corning).

Truemode (Exxelis).

Effect of scanning speed

at a fixed power of 3 W

on the quality of ablation

of Truemode™ polymer

using CW CO2 laser.

Effect of scanning speed at

a fixed 5 W power on the

quality of ablation of

polysiloxane OE4140 /

OE4141 using CO2 laser.

CO2 Laser Machining Trials

CO2 Laser Ablation of Optical Waveguides

(1) (2)

(3)

(4) (5)

FR4

Gaussian beam profile of UV Nd:YAG

laser (5200 model).

UV Nd:YAG Laser Ablation with Stevenage Circuits Ltd

UV Nd:YAG Laser Systems

Investigation

Laser system characterisation.

Waveguide fabrication.

Effects of stage speed, laser power & pulse

frequency were investigated.

Parameter / Model ESI model 5200 ESI Flex 5330

Wavelength (nm) 355 355

Beam profile Gaussian Gaussian & top-

hat

Frequency (kHz) 20 (max.) 70 (max.)

Spot size (µm) 25 (fixed) 53 – 123

(changeable)

Power (W) Up to 2.5

(approx.)

Up to 3.3

(approx.)

Pulse width (ns) 30 60

UV Nd:YAG Laser Ablation Beam Overlap

Issues were

encountered while

overlapping the narrow

beam to form trenches.

Methods to overcome

this was developed.

FR4

FR4

UV Nd:YAG Laser Ablation of Optical Waveguides

Waveguide of 35 µm x 70 µm made in Truemode

material using Flex 5300 model of UV Nd:YAG.

FR4

Upper cladding

Lower cladding

Core

‘Top-hat’ like beam profile (as a result of

mask projection) of Excimer laser trial

Excimer Laser Ablation of Optical Waveguides

Excimer Laser System 248nm Wavelength, Krypton Fluoride (KrF).

20 ns Pulse Length, 1- 40 Hz.

250mJ/pulse (max.) in energy mode or 27kV (max.) in Voltage mode.

Up to 100 mJ/pulse over 1 mm2 at the workpiece.

Investigation Laser system characterisation.

Waveguide fabrication.

Effects of stage translation speed, fluence & frequency were investigated.

Material Truemode (Exxelis).

Polysiloxane OE4140 / OE4141 (Dow Corning).

Square

Mask

Excimer Laser Fabricated Waveguide Structures

Investigations

Speed.

Fluence.

Waveguide width.

Optical density.

Excimer Laser Fabricated Waveguide Structures

Comparison of Laser Processing Methods

Features / Laser CO2 Laser UV Nd:YAG Laser Excimer Laser

Wavelength 10.6 µm (IR) 355 nm (UV). Other

wavelengths available

248 nm (UV). Other

wavelengths available

Beam (polymer

interaction)

Photothermal Photothermal-photochemical Photochemical

Processing speed Very high (e.g.

~100 mm/s)

Moderately high (~10 mm/s) Low (~3 mm/min)

Mask projection No No Yes

PCB process Widely used Widely used -

Mode CW is common but

pulsed also

available.

CW is common in IR

wavelengths but pulsed Q-

switched are common in UV

harmonics.

Mostly in pulsed mode.

Notes

From left to right of the table, there is:

An increase in system capabilities & ablation quality due to the dominance of photochemical

behaviour.

A decrease in processing speed and relative increase in manufacturing cost.

26

Cross-over Waveguide Fabrication

Cross-over waveguides trial

Embedded Mirror Fabrication

450

Optical polymer layer on FR4 substrate



450

45-degree in-plane coupling mirror

design with zero-degree effective turning

angle.

45-degree in-plane coupling mirror

design with 180-degree effective

turning angle.

Embedded In-plane Mirror Fabrication

(1) (2)

(3) (4)

(5) (6)

Embedded In-plane Mirror Fabrication

45-degree in-plane coupling mirror design with zero-degree

effective turning angle.

Project financially supported by the UK Engineering and Physical Sciences Research

Council through the Innovative Electronics Manufacturing Research Centre (IeMRC).

Project partners:

University College London, Loughborough University & Heriot Watt University

Exxelis Ltd (UK), BAE Systems (UK), Cadence (UK), Dow Corning (USA), Stevenage Circuits Ltd (UK), National Physical Laboratory (UK) and Xyratex Technology Ltd (UK).

Particular thanks to Stevenage Circuits Ltd (for giving access to their UV Nd:YAG laser),

and Exxelis Ltd & Dow Corning (for providing optical polymers).

Laser Ablation of Polymer Waveguide and Integrated Mirrors for Optical Circuit Boards

Documents

Transcript of Laser Ablation of Polymer Waveguide and Integrated Mirrors for Optical Circuit Boards