laser micromilling · 2007-08-15 · turning/2d or 3d focused ion beam 200 nm/20 nm 100 nm 20-30...
TRANSCRIPT
October 04 Industrial Business Review
Martyn Knowles
Oxford Lasers Ltd.
Unit 8, Moorbrook Park
Didcot, Oxon OX11 7HP
Tel: +44-1235-814433
Laser Micromilling :
An Enabling Technology for MicroComponent Replication
October 04 Industrial Business Review
Outline
• Introduction
• Process Technologies
• Laser Micro-milling
• Summary
October 04 Industrial Business Review
Micro-manufacturing
• Enabling
Bridging the gap between Nano and Macro
• Disruptive
Change our thinking as to How, When & Where products
will be manufactured and used
• Strategic
Economic, Reduced Space and Energy Costs,
Portability, Productivity
October 04 Industrial Business Review
The Main Challenges in Micro-Manufacture
• Feature sizes below 20 µm
• Tolerances in the range of 1 to
10% of the nominal dimensions
(precision engineering <0.01%)
• Surface roughness required in
the range of 10 to 50 nm that is
smaller than the grain size of
the materialNanotechnology
October 04 Industrial Business Review
Relevant Toolmaking Expertise
Mechanical ProcessesMechanical Processes
•• Micro-Milling Micro-Milling
•• Micro-Turning Micro-Turning
Feature Sizes [Feature Sizes [µµmm]]
2020 0.10.1200200 100100
•• Laser Ablation Laser Ablation
Energy Assisted ProcessesEnergy Assisted Processes
•• Micro-EDM Micro-EDM
•• Ion Beam Machining Ion Beam Machining
October 04 Industrial Business Review
Lasers in Micro-manufacturing
• Established Applications
Via drilling
Hard disk texturing
Lithography
etc
• Factors Enabling Growth
Small features
Wide variety of materials
Flexible
• Factors Limiting Growth
Too slow for mass production (in many but not all cases)
October 04 Industrial Business Review
Serial Production / Parallel Processing / Replication
• Most laser processes employ serial production or
parallel processing
Process speed limited by laser or mechanics/handling
• Laser + Replication Process
Laser
- laser milling to create tool/mold
- process speed unimportant
Replication Process
- high speed, mass production
Enabling Technology
New Laser Applications
October 04 Industrial Business Review
Why Laser Micro-milling?
Laser Micromilling
2.5D or 3D milling by laser ablation
Most materials can be machined
High resolution (very small spot sizes)
Flexible setup,
Easily interfaced with other processes
Easily automated with CAD/CAM software
Main Issues:
Laser choice: laser-material interaction expertise necessary.
Deleterious thermal effects (melt recast, debris deposit)
Post processing sometimes necessary (extra manufacturing step)
Example: 316 s.steel, 1064nm
Lady’s head16 x 10 x 2.5mm
Other micromilling methods:
MicroEDM (material dependent)
Focussed Ion Beam milling (accurate but v. slow)
Lithography (slow, expensive)
www.oxfordlasers.com
October 04 Industrial Business Review
Micro-scale machining comparison
Any1,000 !m3/ sec100 nm100 nm/10 nmPROFIB/2D & 3D
Any>100,000 !m3/secsubmicron5 !m /
submicron
ps laser/2D or 3D
Conductive materials25 millions
!m3/sec
3 !m25 !m / 3 !mMicro-EDM/2D or
3D
Any13,000 !m3/secsubmicron2-4 !m/
submicron
fs laser/2D or 3D
Polymer, ceramics (&
metals)
40,000 !m3/secsubmicron5 !m/ submicronExcimer laser/2D or
3D
PMMA, aluminium,
brass, mild steel
10,400 !m3/sec3 !m25 !m/2 !mMicro-milling or -
turning/2D or 3D
Any20-30 !m3/sec100 nm200 nm/20 nmFocused Ion Beam
(FIB) / 2D & 3D
MaterialsMaterial removal
rate
Feature positional
tolerance
Min. feature
size/ feature
tolerance
Technology/Feature
& geometry
N.B. LIGA can also be used to fabricate parts in polymers, pressed powders, ceramics etc.
October 04 Industrial Business Reviewwww.oxfordlasers.com
Short-Pulse Laser Ablation
100ns 1ns 100ps 1ps
0%
20%
40%
60%
80%
100%
1 2 3 4
Laser
Irradiation
Light
Absorption
Vaporisation
Ablation
Material
Removal
Laser Ablation
- material removal by a combination of evaporation and melt expulsion.
Ejected material (vapour & melt)
Recast (melt) material
Proportion of
evaporation vs melt
At 1J/cm2 courtesy Dausinger et al.
Melt Vapour
October 04 Industrial Business Review
Processing with Ultrashort Pulses
The penetration to which a laser pulse interacts with material is determined by
optical and thermal penetration
L = L op + L th
In dielectrics optical penetration dominates over thermal and for long pulses
strongly depends on wavelength.
In metals, optical penetration is very short (typically tenth of wavelength) and
thermal penetration dominates (function of thermal diffusivity and pulse duration t).
L th = 2 !(K.t) for t >10ps
October 04 Industrial Business Review
Processing with Ultrashort Pulses
Metals
Laser energy is initially absorbed in electrons
Electrons thermalize in about 100fs
Thermal equilibrium between the electrons and lattice occurs after a multiple of the
electron-phonon relaxation time.
Typical electron-phonon relaxation are 0.5 - 50ps.
Simple conclusion from this is that 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 observed in practice and a less simple model explains why.
October 04 Industrial Business Review
Processing with Ultrashort Pulses
Metals
As the lattice heats up evaporation starts and continues for several ns.
Material stays molten for tens of ns
So even for ultrashort pulses, the resulting thermal processes are still in the ns
regime and are almost independent of pulse duration for pulse durations <10ps
Hence the melt layer is never zero but does approach a minimum which is sub-
micron.
There are some effects which depend on pulse duration <10ps and also on pulse
frequency and fluence.
October 04 Industrial Business Review
Processing with Ultrashort Pulses
Dielectrics
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 by Coulomb
explosion and partly thermally.
In metals there is no evidence for Coulomb explosion.
Ultra-high intensity is desirable to enhance the Coulomb explosion in dielectrics
crystals or glass so fs is preferable to ps for processing crystals and glass.
October 04 Industrial Business Review
Summary of Ultrafast Laser Ablation
Metals
- Can be processed with fs and ps sources
- No advantage for fs, certain disadvantages for fs
- 10ps is optimum pulse duration for processing metals.
- Lower fluence improves “quality”
- Higher pulse frequency improves speed and there is no quality degradation when
the fluences are low and/or velocity high.
- Material removal rate for ps laser is > order of magnitude higher than fs because
of intensity and pulse frequency considerations.
Dielectrics - plastics, polymers (inc. teflon)
- High quality results can be achieved with ps and fs sources.
- Shorter wavelengths (eg 355nm) enhance results.
Dielectrics - crystals and glass
- Can be processed with with ps and fs sources.
- Shorter wavelengths (eg 355nm) for the ps source will enhance results.
- Best results probably achieved with fs source
ns laser pulses can also be
used but greater wavelength
dependence and increased
thermal input
October 04 Industrial Business Review
Lasers Used in this Study
cNd:YAG aMP250 aDP100-355 bML Nd:YVO4 bML Nd:YVO4
Wavelength(nm) 1064 511 355 1064 355
Av. Power (W) 100 45 10 10 2
Pulse Freq. (kHz) 4 - 50 5 - 20 0 - 100 0 - 500 0 - 500
Max Energy (mJ) 10 4.5 1 0.3 0.02
Pulse Duration 10µs 17ns 30ns 15ps 12ps
a Oxford Lasers Ltd
b Lumera Laser GmbH
c DMG
October 04 Industrial Business Review
Micro-milling Metals : Stainless Steel
20µm 20µm 20µm
Thick recast
Rough
Many voidsRa=0.86 - 2.20µm
Thin recast
Cracking of recast
layerRa=0.79 - 2.18µm
Recast too thin to
measure
Ra =0.29 - 0.56µm
1064nm, 10 µs 511nm, 17ns 1064nm, 10ps
October 04 Industrial Business Review
Nanosecond Pulse Ablation : Micro-Milling
Polyimide
355nm
Alumina
511nmTungsten
511nm
Diamond
511nm
Examples of optimized processes with nanosecond laser sources
October 04 Industrial Business Review
Nanosecond Laser Drilling :
Special Case of Micro-milling
www.oxfordlasers.com
Alumina 650µm thick
50µm Ø, 60µm pitch
44
45
46
47
48
49
50
1 51 101 151 201 251
Hole Number
Exit
Dia
mete
r [_
m]
Hole Size Repeatability
50µm square holes
entrance
exit
Si3N4 500µm thick, 511nm
90µmØ
October 04 Industrial Business Review
Ceramics – ps Nd:Vanadate Laser
1mm2 square milled with 6 µm raster steps
Scan speed: 300 mm/s
50 kHz, spot size 17µm
Floor surface roughness Ra~0.90 µm
Unirradiated surface roughness Ra~0.73 µm
Surface roughness increases with raster step size
Typical excimer laser removal rate: 105 µm3/s1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0.1 1 10 100
Volume Removal Rate [x107 _m3/sec]
Su
rfa
ce
Ro
ug
hn
es
s,
Ra
[_
m]
Alumina (Al2O3) – 1064nm
100µm 50µm 10µm
www.oxfordlasers.com
October 04 Industrial Business Review
Dielectrics – ps Nd:Vanadate Laser
1mm2 square milled out with 2 µm raster steps
Floor surface roughness Ra~0.99 µm
0.5W, 50 kHz
Scan speed 5-200 mm/s
Milled depth 30-200 µm
100µm100µm500µm
Fused silica - 1064 nm
Some edge chipping present
No evidence for laser induced microcracking
www.oxfordlasers.com
October 04 Industrial Business Review
Dielectrics – ps Nd:Vanadate Laser
2 µm raster steps
Floor surf.roughness
Ra~0.434 µm
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150
Laser Milled Depth [_m]
Su
rfa
ce
Ro
ug
hn
es
s,
Ra
[_
m]
5 µm
Fused silica - 355 nm
www.oxfordlasers.com
October 04 Industrial Business Reviewwww.oxfordlasers.com
Workstation
October 04 Industrial Business Review
General Manufacturing workflow
3D CAD modelling: Tool Design
Structuring of tool topography by FIB, Laser ablation,
mechanical and chemical processes
“hard tooling”
in polymers in metal, quartz or ceramics
moulds/inserts
for µIM
stamps
for HE
templates
for NIL
Replication of polymer, ceramic or glass components
“soft” tooling (pattering of small
patchs of the tool surface including
critical features)
Quality control (SEM, WLI, etc)
CAD model
October 04 Industrial Business Review
Possible Process Chains involving FIB,
Laser ablation, NIL and electroforming
Nano- and micro- structuring of quartz templates
for the S-FIL process
3D CAD modelling: design of quartz template
Micro or nano- pattering of large areas (up to 4”)
in polymers
Transfer the polymer topography in Ni
Ni inserts and tool
integration
FIB,
Laser ablation
NIL
via S-FIL process
Serial production of
polymer components
Hot embossing,
µInjection Molding
Ni plating and
eletroforming
Serial production of Ni
components
October 04 Industrial Business Reviewwww.oxfordlasers.com
Summary
• Micro-machining (laser & non-laser) processes have not yetreached the level of precision (%) achieved in macro-machining
• Laser micro-machining can be an enabling technology but islimited in many cases by throughput.
• Combining laser with other processes e.g. replication, canovercome the throughput problem.
• Ultrafast lasers are an enabling technology for lasermicromilling, especially “difficult materials.”
• Picosecond lasers are a good choice for combination of rangeof materials, machining quality and etch rate.