Micro-Fabrication by ECM and Deposition

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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



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)



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



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.



Micro-tool Fabricated

by Electrochemical Etching

J 30 Qm

J 4 Qm



Micro-tool Fabricated

by Wire Electrical Discharge Machining

W ire E lectrical Discharge Machining

( W E DM)



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



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



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

+-



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.

±



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



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 )


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 )


Period

2 Qs 1 Qs

500 ns 200 ns



(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



(c) 2 Qs period



Hole Size & Shape

According toPu

lse Off-time



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



20 Qm depth

De: 106 Qm, Db: 52 QmTaper: 53Û

50 Qm depth

De: 126 Qm , Db: 66 QmTaper: 31Û

70 Qm depth


100 Qm depth (Through hole)


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



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



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



(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)



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)



(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.



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



Layer-by-layer Machining

Advantage ± Electrolyte flushing for ion

supply

± Short machining time

Machining gap according tomachining time



Micro-mold Fabricatedby Cylindrical Tool

6 V, 60 ns pulse on-time, 1 Qs period



Machining Gap According to Tool Shape

Cylindrical tool

Disk-type tool

6 V, 60 ns/ 1 Qs

?



Disk-type Electrode

Disk-type electrode Material: WC

Disk diameter: 70 Qm

Neck diameter: 20 Qm

100 V, 400 pF



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



Machining GapAccording to Tool Shape

Cylindrical tool

Disk-type tool 6 V, 60 ns/ 1 Qs



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



Electrochemical Milling

Material: SS304


Pulse: 6.0 V, 60 ns / 1 Qs



Micro-groove

Micro-groove (304 SS)

6 V, 60 ns/ 1 Qs45 Qm width, 100 Qm depth, 300 Qm length

300Qm



Micro-wall

Micro-wall

304 SS, 6 V, 60 ns/ 1 Qs

4 Qm width

15 Qm height



Electrochemical Wire Grooving

Material: SS304

Wire: Pt wire 10 Qm


Pulse: 8.0 V, 400 ns / 1 ns

Groove with 28 Qm width, 20 Qm depth



Electrochemical Wire Grooving



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

+ -



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



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



Column Array

3.5 V, 350 ns/1 Qs, 70 Qm height



Micro-spring

2.5 V, 450 ns/1 Qs, 100 Qm spring radius, 350 Qm pitch



Micro Patterning (1)

10 Qm line width, 2.5 V, 400 ns/1 Qs

Cu substrate

Pt-Ir tip



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,



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

Micro-Fabrication by ECM and Deposition

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