lasers and laser systems for micro-machining - ailu · 5 october 04 industrial business review...

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October 04 Industrial Business Review

Lasers and Laser Systems forMicro-machining

Martyn Knowles

Oxford Lasers Ltd

Unit 8, Moorbrook ParkDidcot, Oxfordshire, OX11 7HP

Tel: +44 (0) 1235 810088

www.oxfordlasers.com


Lasers and Laser Systems for Micro-machining

• The Challenges

• Laser Ablation Processes

• Lasers

• Systems

• Software

• Making It All Work

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Micro-Machining

• Features of size 1 - 500 microns in size

• Feature accuracy 0.1 - 5 microns

• Minimize undesirable thermal effects

• Wide range of materials

• Make from bulk material or add features to existing device


Advantages of Laser Micromachining

Genuinely “micro” 1um corner radius<1um surface roughness

Small Heat Effected Zone 0.1 - 2.5um

Many & Difficult materials Aerospace alloysCeramics,glass,Polymers

“Soft” Tooling Fully Programmable Process

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Lasers & Laser Systems

• Easy to use

• Never breaks down

• Can machine all materials

• Very high speed

• Nano-resolution & accuracy

• Low cost

Wish- List


Laser Micro-Machining

Laser Micromachining

is a typical of a new technology

The processes are

– Unfamiliar

– Involve several differentphysical effects

– Only documented inResearch Papers

Design & Specification of the System is Complex & Critical !!

Which Laser ?

Which System ?

Process ?*!

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October 04 Industrial Business ReviewOctober 04 Industrial Business Review

Lasers - Which One?

Frequency

Laser Power(longest wavelength)

Wavelength

Femtosecondsolid state

Picosecondsolid state

Nanosecondsolid state

1064, 532, 355,266nm

50W TEM00

1kW M2~25

0–150 kHz

1064, 532,355nm

1030, 800nm

50W TEM00

0–1000 kHz

25W TEM00

1–5 kHzor

100 - 200kHz

Excimer & F2

157, 193, 248,308, 351nm

500W

0–6 kHz

NOTE : - not all specs achievable simultaneously- solid state harmonic powers significantly less than 1064nm


Laser Systems

• Size

• Ease of use

• Safety

• Stability

• Software

• Motion system

• Automation

• Beam delivery method

• Maintenance

Considerations

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Laser Micro-machining : Parameters

TypeWavelengthOutput PowerPulse EnergyRep.RatePulse LengthBeam DiameterBeam PolarisationBeam Divergence

SpatialTemporal

Beam Intensity Profile

Laser

AbsorptivityReflectivityRefractive IndexSurface Roughness

OPTICAL

Thermal ConductivitySpecific HeatMelting PointBoiling PointEvaporation EnthalpySurface TensionVapour Pressure

THERMOPHYSICAL

DensityHardnessPoisson RatioYoung's Modulus

MECHANICAL

Material

Lens NASpot SizeShot OverlapGas AssistFocal PlaneProcessing SpeedDrilling Technique

Processing

! IMPORTANT: Most parameters are interrelated !!


Laser Micro-Machining

Start by understanding the application andwhat process will meet it.

This defines the laser and systemrequirements.

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October 04 Industrial Business Reviewwww.oxfordlasers.com

Short-Pulse Laser Ablation

100ns 1ns 100ps 1ps

0%

20%

40%

60%

80%

100%

LaserIrradiation

LightAbsorption

Vaporisation

Ablation

MaterialRemoval

Laser Ablation- material removal by a combination of evaporation and melt expulsion.

Ejected material (vapour & melt)Recast (melt) material

Proportion ofevaporation vs melt

At 1J/cm2 courtesy Dausinger et al.

Melt Vapour


Ablation Model

0ns Pulse strikes surface, 1010 W/cm2

5ns Ablating surface temperature reaches 12,000 C

Material is evaporating, producing vapour plume

8ns Incident light strongly absorbed in vapour plume

leading to ionization, i.e. plasma

12ns Heat starts to conduct from plasma into material

30ns Ablating surface is 6,500 C

0.5 µm removed by evaporation

50ns Laser pulse ends, 1.1µm material evaporated

0.5 µs Plasma continues to heat and melt ejection begins

5 µs Temperature now 3000 C and melt ejection ceases

From IndustrialApplications of HighPower CVLs Warner etal.

Pulsed Metal VapourLaser NATO ASI Series

Intense, nanosecond pulse

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Processing with Ultrashort Pulses (ps & fs)

Laser pulse penetration depth determined by optical and thermal properties

L = L op + L th

Dielectrics -optical penetration dominates over thermal

- for long pulses strongly depends on wavelength.

Metals - optical penetration is very short (typically tenth of wavelength)

- thermal penetration dominates

L th = 2 √(K.t) for t >10ps

K = thermal diffusivity, t = pulse duration


Simple Model

- Laser energy is initially absorbed in electrons

- Electrons thermalize in about 100fs

- Thermal equilibrium between the electrons and lattice occurs after a few

electron-phonon relaxation times, ie typically ~10ps.

Simple conclusion

For laser pulses less than the electron-phonon relaxation time then no heat

transferred to lattice, therefore no melt, thermal damage etc.

However, this in not always observed in practice

• evaporation starts and continues for several ns

• during this time there must be some molten material

• so melt layer is never zero but does approach a minimum which is sub-micron.

Processing with Ultrashort Pulses - Metals

Process Optimization canreduce thermal effects

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• Optical penetration dominates over thermal penetration.

• High intensity “rips” electrons out of the lattice.

• Resulting ions repel each other and cause a “Coulomb” explosion.

• Coulomb explosion is a non-thermal ablation mechanism.

• Tests have shown that in dielectrics material is partly removed byCoulomb explosion and partly thermally.

• In metals there is no evidence for Coulomb explosion.

• Ultra-high intensity is desirable to enhance the Coulomb explosion indielectrics crystals or glass so fs is preferable to ps for processing crystalsand glass.

Processing with Ultrashort Pulses - Dielectrics


Which Laser to use?

www.oxfordlasers.com

From P.R. Herman et al.rApplied Surface Science 154–155 (2000) 577–586

Quality Proc.Speed

Laser PowerLaser Rep.RateLaser Focussability

Laser WavelengthLaser Pulse WidthLaser Beam Profile

Important Parameters• feature size• aspect ratio• feature quality• processing speed• cost

Exact shape ofcurve is open to

debate

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Short Pulse Lasers for Micro-Machining

ns ps fs

SapphireGlassPolymersSiliconCeramicsMetals

Deep UV Near UV Visible Near IR

Other factors (speed, quality, cost) further refine choice


Process requirements for different materials

Frequency

Laser Power

Wavelength

MetalsCeramicsPolymers

Excimer or355nm or 266nm

355nm or532nm

1064nmor 532nm

Low Medium -High

Medium -High

5 - 25 kHz0 – 5 kHz 5 - 25 kHz

Drilling or Cutting with Nanosecond Laser

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Laser Micro-machining Systems

Design Principles

Stability - stable frame< 1um pointing accuracy - anti-vibration mounts

Frame - Metal or Granite options

Protection - steel enclosureContaminationAccidental abuseTemperature variation

Safety - interlocked doors- Class 1 safe



Design Principles

Laser - diode pumped solid state- nanosecond or picosecond or femtosecond- 1064, 532, 355 or 266nm- excimer

Motion System - linear, rotary, lift, goniometer axes- up to 32 axes

Options - galvo systems (2 axis and 3 axis)- optical trepanning heads for µdrilling- auto-focus- auto-align- attenuators

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System Options

Automation - Manual load / Pick & Place / Reel to Reel systems etc- Auto-focus

Laser - multi-wavelength systems for advanced processes- multi-laser solutions

Motion System - custom software solutions- CADCAM interfaces- custom 2D calibration

Vision System - on or off-axis viewing- automated alignment- measurement

Diagnostics - in-chuck beam profiler- datalogging of system parameters


Multi-Axis Capability

• Granite base and gantry

• High stability

• Anti-vibration mounting

• Laser and optics on upper gantry

• Motion system on base

• Vision Systems

• XYZ

• Theta & Phi Rotary Axes

• Dual Scan Heads

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Industrial Micro-machining Systems

Nano Second Systems

Alpha Series - Desk Top, R&D

A Series - Entry level, R&D / pilot production

C Series - Shop floor Production system

E Series - Advanced R&D system

G Series - Dual Beam systems

Ultrafast Systems

J Series - Picosecond & Femtosecond systems

Custom Systems

Excimer , Femto, CVL, etc


E Series System

Advanced R&D

• 1.5 ton granite frame

• Class 1 enclosure mounted on floor

• High Power Solid State Laser

• Automated optical attenuator

• Integral laser power meter

• Vision system for alignment / process monitoring

• Cimita software - common across range

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Laser Micro-machining Software

Requirements

• Laser - Control- Fault warning- Data Logging

• Motion Control - XYZ - Galvos - Rotary axes - CADCAM

• Process Control - Attenuators - Auto Focus - Special Processes eg Optical Trepanning

• Vision System - Visual monitoring - Automatic or manual alignment - Measurement

• Automation

Integrated into a single

software package


Cimita Software Suite - Basic Version

Motion

Process Control

Laser

VisionProgramming &

Pre-programmed Routines

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Making It All Work

Most new users of laser micro-machining processes do not have thisexperience.

Who can help ?

• AILU

• Universities & institutes like TWI, TNO, Fraunhofer etc

• Experience system integrators


Micro-Drilling

150 µm diathro’ 1mm

steel

30 degreehole in steel

50 µm diathro’ 0.1mmsteel

150 µm diathro’ 0.5mm

silicon

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Nanosecond Pulse Ablation : Micro-Milling

Polyimide355nm

Alumina511nm

Tungsten511nm

Diamond511nm

Examples of optimized processes with nanosecond laser sources


Micro-Cutting

Diamond

Polyimide

Steel

Silicon

… 20 years experience in laser micromachining

Expert Process Technology

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Removal of ITO from Glass

Patterning -10 micron wide tracks on70 micron pitch

… 20 years experience in laser micromachining



Patterning Thin Films on Flexible Substrates

…20 years experience in laser micromachining


Laser scribed ITO on Flexible Substrate using 532nm (a) 4micron spots with depth of 100nm and (b) scanning five times

slower. Bar denotes 9 microns

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Lasers and Laser Systems for Micro-machining

Conclusions

Laser Micro-machining…..

• Powerful processing tool

• Undergoing Rapid Development

• Wide range of lasers and systems available

• Constant advances in lasers and systems are enabling

new process capability


Advanced Laser Micro-machining Solutions

lasers and laser systems for micro-machining - ailu · 5 october 04 industrial business review...

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