Ultrafast Laser Microwelding using Filamentation - Osaka University

Filament 08, 2nd International Symposium on Filamentation, ENSTA, 32 Boulevard Victor, 75015 Paris, France
September 22 - 25, 2008
Ultrafast Laser Microwelding
using Filamentation
Kazuyoshi Itoh 1 and Yasuyuki Ozeki 1 ,
Takayuki Tamaki 2
1
Osaka University, 2 Nara National College of Technology
1

Outline
-Brief introduction to application of
filamentation
- Ultra-fast laser micro-welding of
transparent and
heterogeneous materials
using filamentation.
Comparison of nano- and femto-second pulses,
Airtight leak test of hermetic ceiling
2

Filamentation
- balancing between self-focusing and defocusing by plasma -
Scattering and/or
luminescence from
filament
Micrograph of the
resultant index
change
Magnified
micrograph
Δn z
= Δn x,y
Δn = 10 -4 ~ 10 -2
3

Applications of filamentation
- Waveguide writing
Waveguides* 1,7 , WG Couplers* 2
- Writing optical elements
Mirrors* 3 , Lenses* 4 , Photonic Devices* 5
- Drilling a hole array * 7
- Welding materials
* 1 K. Yamada, W. Watanabe, T. Toma, K. Itoh, J. Nishii, Opt. Lett. 26, 19 (2001).
* 2 W. Watanabe, T. Asano, K. Yamada, K. Itoh, J. Nishii, Opt. Lett. 28, 2491 (2003).
* 3 K. Yamada et al, Jpn. J. Appl. Phys., 42, Part 1, 6916(2003).
* 4 K. Yamada, W. Watanabe, Y. Li, K. Itoh, and J. Nishii, Opt. Lett,. 29, 1846 (2004) .
* 5 Y. Li, W. Watanabe, T. TamakiI, J. Nishii, and K. Itoh, J. J. Appl. Phys., . 44, 5014 (2005).
* 6 S. Sowa, W. Watanabe, T. Tamaki, J. Nishii, and K. Itoh, Appl. Phys. A, 81,1587 (2005).
* 7 S. Sowa, W. Watanabe, T. Tamaki, J. Nishii, and K. Itoh, Opt. Express 14, 291-297 (2006).
4

- Ultra-fast laser micro-welding
of glass with filaments
T. Tamaki, W.Watanabe, J. Nishii, and K. Itoh, Jpn. J. Appl. Phys., Vol. 44, L687-L689 (2005).
T. Tamaki, W.Watanabe, and K. Itoh, Optics Express, Vol. 14, Issue 22, 10460-10468 (2006).
W. Watanabe, S. Onda, T. Tamaki, and K. Itoh, Appl. Phys. B, Vol. 87, pp. 85-89 (2007).
5

Scanning the filament
Low repetition source
Fast scanning
~ Gap
High repetition source
~ Accumulation of heat
Low repetition
Slow scanning
~ No gap
6

Optical setup
Samples
Fixture
Setup
· Wavelength: 800 nm
· Pulse duration: 130 fs
· Repetition: 1 kHz
· Incidence energy: ~ 1.0 µJ/pulse
Fixture
· Numerical aperture: 0.30
· Irradiation area: 100 µm x 100 µm
· Translation speed: 5.0 µm/s
7

Micrographs of welded silica glass samples
Schematic
Top view
Side view
8

Joining strength (Same material)
Pulse Energy [µJ/pulse]
10
5
15.4
MPa 14.9
MPa
14.9
MPa
0.01
15.3
MPa
15.2
MPa
15.1
MPa
15.2
MPa
15.0
MPa
14.9 MPa
14.9
MPa
14.9
MPa
0.1 1
Scanning Speed [mm/s]
Map of joining strength
Borosilicate glass
Fused silica glass
- 15 MPa ~ 153 kgf/cm 2
- Usual adhesive ~ 50 kgf/cm 2
(kgf: kilogram force)
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Optical transmittance
81.4 %
85.9 %
87.0 %
Pulse Energy [µJ/pulse]
10
5
86.0 %
87.1 % 88.2
89.0 %
%
0.01
86. 8
%
86.7 %
87.3 %
87.1
%
0.1 1
Scanning Speed [mm/s]
Borosilicate glass
81 ~ 87 %
Theoretical limit: 92 %
Fused silica glass
87 ~ 89 %
Theoretical limit: 93 %
10

Heterogeneous welding:
10
Pulse Energy
[µJ/pulse]
1
0
15.3 MPa 14.9 MPa
15.2
MPa
15.1
MPa
15.2
MPa 15.0
MPa
14.9
MPa
14.9 MPa
15.0
MPa
14.9
MPa
0.1 1
Scanning Speed [mm/s]
Map of joining strength
dissimilar kinds of glass
Laser
Pulses
Geometry
Borosilicate glass
39* [×10 ‐ /
Fused silica glass
5.9* [×10 ‐ /
*Thermal expansion coefficient
Wataru Watanabe, Satoshi Onda, Takayuki Tamaki,
Kazuyoshi Itoh, and Junji Nishii,
Appl. Phys. Lett., Vol. 89, No. 2, 021106 (2006).
11

Joining strength and transmittance
15.3 MPa 14.9 MPa
71.5 %
73.2 %
10
15.1
MPa
15.0
MPa
10
72.6 % 73.0 %
Pulse Energy
[µJ/pulse]
15.2
MPa
15.0
MPa
14.9
MPa
Pulse Energy
[µJ/pulse]
71.8 %
73.0 %
73.4 %
15.2
MPa
14.9
MPa
72.1 %
73.6 %
14.9
MPa
0.1 1
Scanning Speed [mm/s]
88.3 %
0.1 1
Scanning Speed [mm/s]
Joining strength
Optical transmittance
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Effects of Annealing ( silica glass & silica glass)
Welded part
Micrograph
before annealing
100 µm 100 µm
Micrograph
after annealing
Annealing makes welded part invisible.
(Implication of disappearance of defects.)
13

Enhancement of joining strength &
optical transmittance
Joining strength Borosilicate glass Fused silica glass
Before
annealing 15 MPa 15 Mpa
After
annealing 33 MPa 33 MPa
Optical transmittance
Before
annealing 88 % 87 %
After
( 336 kgf/cm 2 )
annealing 92 % 91 %:
(Theoretical limit: 93 %) (Theoretical limit: 92 %)
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Enhancement of optical transmittance
by annealing
Borosilicate glass
Fused silica glass
Before
annealing 88 % 87 %
After
annealing 92 % 91 %
(Theoretical limit: 93 %) (Theoretical limit: 92 %)
15

- Ultra-fast Laser Micro-welding of
Glass and Copper
Y. Ozeki, T. Inoue, T. Tamaki, H. Yamaguchi, S. Onda, W. Watanabe, T. Sano,S. Nishiuchi,
A. Hirose, and K. Itoh, Appl. Phys. Express, vol.1, p. 082601, (2008).
K. Itoh and T. Tamaki, SPIE Commercial and Biomedical Applications of Ultrafast Lasers VIII,
Invited Paper, San Jose Convention Center, San Jose, CA. 20 - 23 January 2008.
K. Itoh and T. Tamaki, PICALO 2008, The 3 rd Pacific International Conference on Application of
Lasers and Optics, Invited Paper, April 16 - 18, Capital Hotel, Beijin China, 2008.
16

Heterogeneous welding:
Material
*Thermal expansion coefficient
Polymer
Semiconductor
Metal
Alloy
PMMA
700 [×10 ‐ /
Silicon
28 [×10 ‐ /
Cupper
183 [×10 ‐ /
Stainless steel
175 [×10 ‐ /
dissimilar kinds of materials
Fused silica glass
5.9 [×10 ‐ /
Successful
Borosilicate glass
39 [×10 ‐ /
Geometry
Wide range of heterogeneous welding
17

Ultra-fast Laser Micro-welding of Glass and
Copper
Realizing tight contact
between
glass and copper
18

(a) Side view (b) Top view (c) Whole image
Optical microscope images
Laser source: Regenerative Ti:sapphire laser
(Spectra Physics, Spitfire)
Central wavelength: 800 nm
Pulse duration: 130 fs
Repetition rate: 1 kHz
Pulse energy: 4 µJ/pulse
Scan speed: 1 mm/s
Joining strength:
~20 MPa
19

Joining Strength &
Electron Micrograph of Interface
Joining Strength [MPa]
0.4 µJ Average: 21.5 MPa
40
35
30
25
20
15
10
5
0
0.1 1 10
Pulse Energy [µJ]
Glass
Copper
1 µm
No crack nor gap observed but
some bumpy irregularity presents.
20

Comparison with ns-pulse welding
30
Joint strength [MPa]
20
10
Femtosecond
pulse
Nanosecond
pulse
< 1/100 reduction
0
10 -1 10 0 10 1 10 2
Pulse energy [µJ]
Lower energy welding is possible by using fs pulses.
Femtosecond pulse: 800 nm, 130 fs, 1 kHz
Nanosecond pulse: 527 nm, 600 ns, 1 kHz
Translation speed: 1 mm/s
21

Sample morphology
200 µm
Nanosecond pulse welding
(527 nm, 600 ns, 50 µJ,
1 kHz, 1 mm/s)
Femtosecond pulse welding
(800 nm,

Difference of heat sources
Femtosecond pulses
Nanosecond pulses
Glass
Nonlinear absorption
in filament
(Heating)
Glass
No filament
No absorption
(No heating)
Metal
Linear absorption
(Heating)
Metal
Linear absorption
(Heating)
23

Application of Ultra-fast Laser Micro-welding
to Metal Package (Glass & Kovar)
(a) Birds-eye view
(b) Top view
24

Hermetic ceiling of ceramic package
Schott D263 glass
50µm
Ceramic cabity
Electroless
nickel plating
Ceramic package
(92% Alumina)
Welded part
25

Leakage test
Group
1
2
3
The results are almost perfect.
26

Summary
-Ultra-fast laser micro-welding of
homogeneous and heterogeneous materials
- silica glass and copper
average joining strength: 21.5 Mpa
( ~220 kgf/cm 2 )
- filaments alleviates the focusing requirements
and acts as an important source of
heat for welding.
50µm
27

Coworkers:
Dr. Wataru WATANABE,
Dr. Junji NISHII
National Institute of Advanced Industrial Science
and Technology
Mr. Satoshi Onda
Yokogawa Electric Corporation
Mr. Seiji Sowa
Konica Minolta Opto, Inc.
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