Electrochemical Machining
rate of electrolyte movement in the tool washes
metal ions away from the work piece (anode) before
they have a chance to plate onto the tool (cathode)
-removal rate (MRR) in ECM is
Electrical-discharge Machining
materials involved
discharges
higher is the wear rate
-conducting wires are allowed to
touch each other, an arc is produced
small portion of the metal eroded away and leave a
small crater
Principle of Operation
workpiece, connected to a DC power supply and
placed in a dielectric fluid
breaks down and a transient spark discharges
through the fluid, removing a small amount of metal
Process Capabilities
polarity and using copper tools
Design Considerations for EDM
1. Parts should be designed so that the required
electrodes can be shaped properly and economically
2. Deep slots and narrow openings should be avoided
3. The surface finish specified should not be too fine.
4. Bulk of material removal should be done by
conventional processes
Process Capabilities
Electron-beam and Ion-beam Lithography
ctronbeam (e-beam) and ion-beam (i-beam)
lithography is superior to photolithography in
terms of attainable resolutions
in narrow electron or ion beams which scan a pattern
one pixel at a time onto a wafer
Scan time increases as the resolution increases, as
more highly focused beams are required
Etch rate calculation (interpolation)
If a square mask side length 100 micron is placed on
(1,1,1) plane and oriented with a side in the (1,1,1)
direction. Based on the figure calculate the time to
etch of an 8 micron at 60 degree using ethylene.
Sketch the resulting profile.
relative movements of the workpiece in relation to
the electrode
conductor
-removal rate can be estimated from
surface finish with poor surface integrity and low
fatigue properties
EDM Calculation
A 45mm thick copper plate is being machined by wire
EDM. The wire moves at speed of 100mm/min & the
kerf width is 0.18mm. Find the MRR & mass removal,
if the density of copper is 600kg/m3. Calculate the
required power if it takes 3000J to melt one gram of
copper.
1) MRR = kerf x thickness x speed
= 0.18mm x 45mm x 100mm/min = 810mm3/min
@810x10-9 m3/min
2) Mass Removal Rate = Density x MRR
= 600kg/m3 x 810x10-9 m3/min
high strength materials
turbine blades, jet-engine parts and nozzles
on of ECM, shaped-tube electrolytic
machining (STEM), is used for drilling small-diameter
deep holes
-free, bright surface and
can be used as a deburring process
centers with high production rates, high flexibility,
and close dimensional tolerances
=
Dielectric Fluids
1. Act as an insulator until the potential is sufficiently
high
2. Provide a cooling medium
3. Act as a flushing medium and carry away the
debris in the gap
Electrodes
copper–tungsten alloys
metallurgy, or CNC machining techniques
workpiece material removed to the volume of tool
wear
4.86𝑥10−4 𝑘𝑔/𝑚𝑖𝑛
60
𝑥 1000 = 0.0081𝑔𝑟𝑎𝑚/𝑠
3) Power = mass removal rate x P
= 0.0081gram/s x 3000 J/gram = 24.3 J/s
Photolithography
Extreme Ultraviolet Lithography
a = y1 – y2 (distance) = 4 b = y3 – y1 = 12
y1 = 10-2 = 0.01, y2 = 10-1 = 0.1, y3 = 100 = 1
𝑎
4
𝑥 (𝑦3 − 𝑦1 ) + 𝑦1 =
𝑥 (1 − 0.01) + 0.01
𝑏
12
= 0.34𝜇𝑚/ℎ
𝑑𝑒𝑝𝑡ℎ
8𝜇𝑚
𝑡𝑖𝑚𝑒 =
=
= 23.53ℎ
𝑒𝑡𝑐ℎ 𝑟𝑎𝑡𝑒 0.34𝜇𝑚/ℎ
Identify etch rate and calculate time to etch silicon
dioxide lamp, layer 1 = 10micron & layer 2 = 1micron.
Etch material: concentrated HF 49%
immersion lithography is limited by light diffraction
at a wavelength of 13 nm
Layer 1 = 10µm (10x10-6), Layer 2 = 1µm (1x10-6)
molybdenum–silicon mirrors which absorb EUV
light, through the mask to the wafer surface
X-ray Lithography
superior to photolithography as it has shorter
wavelength of the radiation and the very large
depth of focus
is less susceptible to dust than photolithography
Etch rate = 2300x10-9 m/min = 2.3 x10-6 m/min
Thickness = 10 µm + 1 µm = 11 µm
𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
11𝜇𝑚
𝐸𝑡𝑐ℎ 𝑟𝑎𝑡𝑒 =
=
= 4.78𝑚𝑖𝑛
𝑒𝑡𝑐ℎ 𝑟𝑎𝑡𝑒 2.3𝜇𝑚/𝑚𝑖𝑛
Reactive Plasma Etching
Surface Micromachining
plasma etching and other molecular
species diffuse into and chemically react with the
substrate
illustrated for silicon devices
step (using sulfur hexafluoride, SF6) laterally etches
the exposed sidewalls at the bottom of the trench.
This undercut (when it overlaps adjacent undercuts)
releases the machined structures.
SIMPLE
vacuum system
current is passed through it
bulk micromachining
In CAIBE, ion bombardment can assist dry
chemical etching by:
1. Making the surface more reactive
2. Allowing the chemically reactive species access
to the cleared areas
3. Providing the energy to drive surface chemical
reactions
Bulk Micromachining
-dependent
etches on single-crystal silicon
etching down into a surface and
stopping on certain crystal faces, doped regions,
and etchable films to form a desired structure
acer layer must
be selected carefully
be overcome is stiction
after wet etching
liquid etchant is dried from the wafer surface
SCREAM
doped silicon and the patch will not be etched
Another method for making very deep MEMS
structures is the SCREAM (single-crystal silicon
reactive etching and metallization) process, depicted
in Fig. In this technique, standard lithography and
etching processes produce trenches 10 to 50 µm
deep, which are then protected by a layer of
chemically vapor deposited silicon oxide. An
anisotropic-etching step removes the oxide only at
the bottom of the trench, and the trench is then
extended through dry etching. An isotropic etching
An alternative to SCREAM is the SIMPLE (silicon
micromachining by single-step plasma etching)
technique, as depicted in Fig. This technique
uses a chlorine-gas-based plasma-etching process
that machines p-doped or lightly doped silicon
anisotropically, but heavily n-doped silicon
isotropically. A suspended MEMS device can thus be
produced in one plasma-etching device, as shown in
the figure. Some of the concerns with the SIMPLE
process are as follows:
° The oxide mask is machined, although at a slower
rate, by the chlorine-gas
plasma. Therefore, relatively thick oxide masks are
required.
° The isotropic etch rate is low, typically 50 nm/min.
Consequently, this is a very slow process.
° The layer beneath the structures will have
developed deep trenches, which may affect the
motion of free-hanging structures.
Nanoscale Manufacturing
Top-down approaches use large building blocks (such
as a silicon wafer) and various manufacturing
processes (such as lithography, and wet and plasma
etching) to construct ever smaller features and
products (microprocessors, sensors, and probes).
-down approaches:
1. Photolithography
2. Nanolithography
3. Dip Pen Nanolithography
Bottom-up approaches use small building blocks
(such as atoms, molecules, or clusters of atoms and
molecules) to build up a structure.
-up approaches include:
1. Dip pen nanolithography
2. Microcontact printing
3. Scanning tunneling microscopy