1. Lecture 2 Fundamentals of Multiscale Fabrication
Multiscale fabrication I:
Conventional machining
Kahp-Yang Suh
Associate Professor
SNU MAE

2. Mechanical machining based on molds
Compression molding (> 1mm)
Injection molding (> 1mm)
Extrusion (> 1mm)
Stereolithography (> 100 nm)
Electrical Discharge Machining (> 50 m)
LIGA process (1 mm ~ 10 m)
Photolithography (> 60 nm)
Imprinting (10 m ~ 10 nm)
Capillary molding (100 m ~ 50 nm)

3. Compression molding
- Fabricating replica of a mold on a melted plastic.
Platen
Mold Plunger
Guide Pins
Mold Cavity
Hydraulic Plunger
Heat and Cooling
Hydraulic Pressure
Compound to be molded

4. Injection molding - Turning plastic stock into finished products.
Hydraulic
Pressure
Nozzle
Feed hopper,
contains polymer pellets

5. Cores for cooling water
Extrusion
- Fabricating tubes or films from a die.
Feed hopper
Heaters
Cores for cooling water
Die
Screw
Drive shaft

6. Stereolithography
- A family of unique fabrication processes developed to make engineering prototypes in minimum lead time based on a CAD model of the item (cf. Rapid Prototyping).
World’s smallest ox (10m) fabricated by femto-second laser stereolithography

7. Electrical Discharge Machining (EDM)
- Using electricity to remove metal by spark erosion.

8. LIGA Process (1)
The LIGA process was developed at the IMT (Institute of Microstructure Technology), in the early eighties under the leadership of Dr. W. Ehrfeld.
LIGA is a German acronym for Lithographie, Galvanoformung, Abformung (lithography, galvanoforming, molding)
High aspect ratio > 20
High accuracy < 0.5 m
High uniformity

9. LIGA Process (2)
Epoxy resin is selectively cured by X-ray beamed through a mask.
Uncured epoxy is etched away.
Subsequent masking steps produce additional features.
Metal is then electroformed over the cured epoxy to form a mold half.
The metal mold is ground to the correct height, and the epoxy is dissolved away, leaving a cavity and ejector holes.
The tool is ready to mold parts.

10. LIGA Process (3)
LIGA examples

11. Photolithography (1)

12. Photolithography (2) Well-established technique
UV light
Mask
Photoresist
Well-established technique
Two dimensional patterning
Expensive materials and
equipment
Limitations for feature sizes
less than 50 nm
Developing
Etching
Stripping

13. (Reactive ion etching)
Nanoimprint lithography (NIL)
(Prof. Steven Y. Chou, Princeton University)
Mold
Substrate
200nm dots
Polymer
Mold preparation
Polymer coating
Pressing
Pattern transfer
(Reactive ion etching)

14. Capillary molding Place the mold on the polymer surface Heating
PDMS mold
Polymer
Place the mold on the polymer surface
Substrate
Heating
(T > Tg)
Cooling and mold removal
Meniscus
Thick film
Thin film
Patterning by temperature-directed capillarity

15. Results of capillary molding
Thick and Thin polymer films
Complex and Large-area patterning
Film thickness:
1.5 m
Polystyrene, 130ºC, 6 hrs
Film thickness:
180 nm
Styrene-Butadiene-Styrene copolymer
120C, 1 hr

16. Ultra-Short Pulse Laser Material Processing
ns Machining Process
fs Machining Process ns fs
Steel foil
100 m in thickness

17. Atomic Force Microscope + Near Field Optics (NSOM)
Nano-Machining
Atomic Force Microscope + Near Field Optics (NSOM)
Nanodots
Nanocurves
Nano-lithography/machining
Nanogrids
~10 nm