micro-fabrication by ecm and deposition
TRANSCRIPT
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Microfabrication by ElectrochemicalMachining and Deposition
Byung Jin Park
Prof. Chong Nam ChuSchool of Mechanical and Aerospace Engineering
Seoul National University, Korea
September 9, 2004
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Characteristics of Micro-E
CM
No tool wear (vs. EDM, Micro end milling)
No mechanical stress (vs. Micro end milling)
No heat affected zone (vs. EDM, Laser beam machining)
Excellent surface quality
3D complex shape (vs. Lithography)
Versatility of materials: metal, conductive polymer, graphite,
semiconductor, etc. (vs. Lithography)
Low cost (vs. Lithography, Ion beam machining, LIGA) Good productivity (vs. AFM/STM manipulation, Ion beam machining)
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Research
Contents
Micro-tool fabrication
Electrochemical etching
Wire electrical discharge
machining
E lectrochemical machining
Micro-hole
Micro-groove
Micro-mold
E lectrochemical deposition Micro-column
Micro-spring
Micro patterning
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Electrochemical Etching
H2SO4 solution
Z-stage
PMACcontroller
Feedingdirection
Pt wire
Tungstencarbide
DC power supply
PC
S chematic diagram of the ECE system
Electrochemical etching of WC rod (high rigidity & high
hardness)
Electrolyte: 1.5 M H2SO4
solution
Shaft size, shape, and
surface quality according toelectrolyte concentration,
applied voltage, etching time,etc.
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Micro-tool Fabricated
by Electrochemical Etching
J 30 Qm
J 4 Qm
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Micro-tool Fabricated
by Wire Electrical Discharge Machining
W ire E lectrical Discharge Machining
( W E DM)
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Principle of Electrochemical
Machining/Deposition
Workpiece
Tool
Machining: anodic dissolution
Deposition: cathodic reduction
Electric field localization at tool-end
region using ultra short pulses
Electrolyte
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Principle of Electric Field
Localization Using Ultra ShortPu
lses
T ip-end of a tool : due to small electrolyte resistance (Rs_small),the time constant (X1) for double layer charging is small.
S ide of a tool : due to large electrolyte resistance (Rs_large
), thetime constant (X2) for double layer charging is large.
Dissolution region can be localized under the condition of
X1 <T<< X2 (T: pulse on-time)
X= Vd C DL
d : machinable distance
V: specific electrolyte resistivity
C DL: specific double layer capacity (~10 QF/cm2)
X: time constant for DL charging
Rs_large
Rs_small
C
d
Tool
Workpiece
Rp
T
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TARBO 8551
Pulse Generator
(50MHz)
TDS 3034Oscilloscope
(300MHz,Tektronix)
Experimental Equ
ipments
Tool
Workpiece
BalanceElectrode
Pulse Generator
Oscilloscope
PMAC Controller
S chematic diagram of pulsed EC M system
+-
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B
alance Electrode
+
Vwork
Vtool
surface covered with chromium oxide layer after machining without balance electrode
Because of very small contact area between thetool and the electrolyte, the voltage drop israther larger than the voltage drop betweenelectrolyte and substrate.
Cr passive layer (chromium oxide) is formed onthe hole surface.(Cr passivation region: -300 mV~1000 mV)
By implementing the balance electrode (Ptplate) connected to the cathode, we canmachine the holes in the transpassive region.- Minimize the bubble generation, boiling.
- Prevent the Cr oxide layer forming.
±
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Experiments for Dissolu
tion Localization
Feeding 10 Qm into the workpiece
Machining for a specific time
Measuring the hole diameter atthe top surface
J 30 Qm
10 Qm
R 5 Qm
Electrolyte 0.1 M H2SO4
Tool WC J 30 Qm
Workpiece 304 SS
Pulse period 2 Qs
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0 10 20 30 40 50 60
30
40
50
60
70
80
o l
i
t r ( Q
)
c i i Ti ( i )
¡
-ti¢ £
20 ¡
s 40 ¡
s
60 ¡
s 80 ¡
s
C 3.5V 5.0 V, 2 Qs p riod
6.0 V, 2 Qs p riod 6.0 V, 40 s on-ti
Localization According toPu
lse On/Off-time and Applied Voltage
0 30 60 90 1200
200
400
600
800
1000
1200
H o
l e D i a m e t e r ( Q m )
Machining Time (min)
0 10 20 30 40 50 60
30
40
50
60
70
80
H o l e D i a m e t e r
( Q m )
Machining Time (min)
On-time
20 ns 40 ns
60 ns 80 ns
0 10 20 30 40 50 60
30
40
50
60
70
80
H o l e D i a m e t e r
( Q m )
Machining Time (min)
Period
2 Qs 1 Qs
500 ns 200 ns
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(a) 200 ns period
J 30 Qm tool, 6.0 V,40 ns on-time,
30 min. machining time,55 Qm diameter.
(b) 5 00 ns period
J 30 Qm tool, 6.0 V,40 ns on-time,
30 min. machining time,49 Qm diameter.
(c) 2 Qs period
J 30 Qm tool, 6.0 V,40 ns on-time,
30 min. machining time,47 Qm diameter.
Hole Size & Shape
According toPu
lse Off-time
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Two Step Condition
Step 1: J30 Qm tool
6.5 V, 120 ns/2 Qs
40 min machining time
85 Qm depth
84 Qm diameter
Step 2: J30 Qm tool
5.0 V, 30 ns/2 Qs
20 min machining time
15 Qm depth
28 Qm diameter
T his process can be applied to fabricate the micro-punching dies and nozzles
Front Back
StepH
ole
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20 Qm depth
De: 106 Qm, Db: 52 QmTaper: 53Û
50 Qm depth
De: 126 Qm , Db: 66 QmTaper: 31Û
70 Qm depth
De: 132 Qm , Db: 72 QmTaper: 23Û
100 Qm depth (Through hole)
De: 140 Qm , Db: 108 QmTaper: 9Û
Over-cut generation Large taper
Gradual decrease in taper angledue to increased machined depth
Sudden reductionin taper just after
perforation
J 50 Qm tool, 7.5 V, 300 ns / 2 Qs, without balance electrode
The Sequence of Taper
Generation
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Mac ining Ti
H o l
i a .
1> 2
Entr anc
Bottom
Mac ining start E1
Mac ining start B1
T_f d T_dw ll
E2
B2
TVoltage up
On-time up
1 2
Tfeed Tdwell
T
D1
D2
B1
B2
E1
E2
T
Ehigh : Entrance, High Condition
Elow : Entrance, Low Condition
Bhigh : Bottom, High Condition
Blow : Bottom, Low Condition
Taper ReductionT
echniqu
e inB
lindH
ole Machining
Localization
Curve
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J 20 Qm tool, 100 Qm thickness 304 SS
(a) Continuous condition :6.0 V, 80 ns on-time, 2 Qs period, 20 minmachining time
60 Qm depth, 49 Qm diameter and 12.7Û taper
angle.
(b) Two-step condition :1st step: 6.0 V, 80 ns on-time, 2 Qs period, 30min machining time
2nd step: 7.0 V, 100 ns on-time, 2 Qs period, 5min machining time
60 Qm depth, 52 Qm diameter and 4.8Û taper
angle.
Taper Reductionby the Proposed Method
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(a) Entrance: 13.6 Qm in diameter (b) Exit: 10.5 Qm in diameter
Two step condition :
1st step: 4.8 V, 32 ns/2 Qs, 50 min machining time.
2nd step: 5.2 V, 32 ns/2 Qs, 10 min machining time.
t 100 304 SS, 0.1 M H2SO4, J 4 Qm tool
J 13.6 Qm / J 10.5 Qm, 0.9Û taper angle,
A/R 8.3
Micro-hole (1)
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t 100 Qm 304 SS, 0.1 M H2SO4, J 4 Qm tool
(a) Entrance: 20.3 Qm in diameter (b) Exit: 18.1 Qm in diameter
Two step condition :
1st step: 5 V, 30 ns/2 Qs, 25 min machining time.
2nd step: 5.5 V, 30 ns/2Qs, 10 min machining time.
J 20.3 Qm / J 18.1 Qm, 0.6Û taper angle,
A/R 5.2
Micro-hole (2)
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(a) Entrance: 8.0Qm in diameter (b) Exit: 7.3 Qm in diameter
t 20 Qm 304 SS, 0.1 M H2SO4, J 6 Qm tool
J 8.0 Qm / J 7.3 Qm, 1.0 º taper angle and A/R 2.3
Micro-hole (3)
4.2 V, 21 ns/2 Qs, 30 min machining time.
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Micro-mold Fabrication byElectrochemical Milling
Material: Stainless steel (304 SS)
Mold size:
150 mm x 100 mm x 60 mm
Column size:
30 mm x 20 mm x 60 mm
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Layer-by-layer Machining
Advantage ± Electrolyte flushing for ion
supply
± Short machining time
Machining gap according tomachining time
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Micro-mold Fabricatedby Cylindrical Tool
6 V, 60 ns pulse on-time, 1 Qs period
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Machining Gap According to Tool Shape
Cylindrical tool
Disk-type tool
6 V, 60 ns/ 1 Qs
?
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Disk-type Electrode
Disk-type electrode Material: WC
Disk diameter: 70 Qm
Neck diameter: 20 Qm
100 V, 400 pF
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Micro-mold with a Vertical Column
Micro-mold (304 SS)
6 V, 60 ns / 1 Qs
Column size
± Width: 30 Qm
± Height: 60 Qm
10Qm
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Machining GapAccording to Tool Shape
Cylindrical tool
Disk-type tool 6 V, 60 ns/ 1 Qs
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Micro-mold Fabricated by Disk-typeTool
Micro-mold (304 SS)
6 V, 60 ns pulse on-time, 1 Qs
period Column size
± Width: 84 Qm
± Height: 80 Qm
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Electrochemical Milling
Material: SS304
Electrolyte: 0.1 M H2SO4
Pulse: 6.0 V, 60 ns / 1 Qs
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Micro-groove
Micro-groove (304 SS)
6 V, 60 ns/ 1 Qs45 Qm width, 100 Qm depth, 300 Qm length
300Qm
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Micro-wall
Micro-wall
304 SS, 6 V, 60 ns/ 1 Qs
4 Qm width
15 Qm height
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Electrochemical Wire Grooving
Material: SS304
Wire: Pt wire 10 Qm
Electrolyte: 0.1 M H2SO4
Pulse: 8.0 V, 400 ns / 1 ns
Groove with 28 Qm width, 20 Qm depth
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Electrochemical Wire Grooving
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Electrochemical Deposition
0.5 M CuSO4
0.5 M H2SO4
Cu substrate
Pt-Ir tip
Pulse generator
Oscilloscope
PMAC controller
Electrochemical deposition of
Cu on Cu substrate
Electrolyte: 0.5 M CuSO4 + 0.5M H2SO4 solution
Deposition size, shape, and
structure according to appliedvoltage, and pulse duration
Electrochemical writing
Cathode: Cu2+ + 2e ± Cu
Anode: 2H2O 4H+ + 4e ± + O2
Ex perimental set-up for
electrochemical deposition
+ -
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Effects of Applied Voltage& Pulse On-time on Deposition
2.5 3.0 3.5 4.0 4.5 5.0
6
8
10
12
14
16
18
20
On-time: 400 ns
Pulse period: 1 Qs
C o l u m n D i a m e t e r (
Q m )
Voltage (V)
Deposited column diameter
decreases as applied voltageincreases since the growing rate is
high under high voltage condition
Dendritic structure is formed withshort pulse on-time (< 250 ns /1 Qs)
Column diameter according to
applied voltage
Applied voltage: 3.0 ~ 3.5 V
Pulse: 350 ~ 450 ns / 1 Qs
R ecommended condition
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Column Deposition
3.5 V, 450 ns/1 Qs, J 7 Qm dia., 24 Qm
height
4.0 V, 450 ns/1 Qs, J 7 Qm dia., 15 Qm
height
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Column Array
3.5 V, 350 ns/1 Qs, 70 Qm height
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Micro-spring
2.5 V, 450 ns/1 Qs, 100 Qm spring radius, 350 Qm pitch
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Micro Patterning (1)
10 Qm line width, 2.5 V, 400 ns/1 Qs
Cu substrate
Pt-Ir tip
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Micro Patterning (2)
10 Qm line width, 2.5 V, 450 ns/1 QsSpiral, line width 15 Qm, pitch 60 Qm,
2.0 V, 450 ns/1 Qs,
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Conclusions
Micro-tool Fabrication
Electrochemical Etching Wire Electrical Discharge Machining
Localization of Electrochemical
Reaction
Region, Using UltraShort Pulses
Machining Gap Modeling, Tool Shape Design
Electrochemical Machining
Micro-hole
Micro-groove
Micro-mold Electrochemical Deposition
Micro-column Micro-spring
Micro patterning