Hot Embossing Lithography

1
Experimentation for Heating Parameter Design and
PMMA Characterization on a Hot Embossing Set-up
2
Heating Experiments

• Objective
• Check uniformity of heating.
• Record the time to heat a block to a certain
  temperature (200 deg C).
• Compare experimental results (uniformity and
  time) with ANSYS analysis.
• Extrapolate results for the original heating
  blocks.

3
Experimental Setup

• Heating mode Heating cartridges (Power 1kW).
• Specimen Two-hole and four-hole blocks.
• Temperature sensor J type Thermocouple.
• Data Acquisition and monitoring LabVIEW.
• Miscellaneous Relays, power source, etc.

4
Experimental Setup (Cont..)
5
Thermal Analysis (Heating)
Temperature distribution for the experimental
block with two heating cartridges
Thermocouple locations on the block
6
Temperature Profile (Heating)
Comparison of temperature profile obtained at
location 7 from thermal analysis and experimental
data
7
Temperature Difference (Heating)
Temperature difference plot between thermocouple
locations 8 and 3
8
Temperature Profile (Cooling)
Temperature profile at thermocouple location 7
during cooling (volume flow rate of 0.52 gpm of
water)
9
Temperature Difference (Cooling)
Temperature difference plot between thermocouple
locations 1 and 4
10
PMMA Characterization

• Objective
• Obtain stress-strain curves for Poly methyl
  methacrylate (PMMA) at different temperatures.
• Calculate Youngs modulus from the available
  data.
• Find glass transition temperature PMMA.

11
Important Embossing Parameters

• Temperature of embossing
• Viscosity of the polymer is directly proportional
  to the temperature.
• Pressure
• Embossing pressure depends on the depth of
  embossing.
• Speed of embossing
• Speed of embossing controls flow of the polymer.

12
PMMA Properties

• Stress strain curves are nonlinear.
• Glass transition temperature has significant
  effect in properties of PMMA.
• At elevated temperatures
• Modulus (Compressive) values drop.
• Compressive strength drops.
• Creep effects increase.

13
Stress-Strain Curve
Stress-Strain curve for PMMA obtained using a
cylindrical tool of 1 diameter
14
E variation with Temperature
Variation of Youngs Modulus with temperature
obtained using two different tool sizes
15
Specimen Pictures
16
Conclusions

• Experiments show good temperature uniformity on
  the experimental block.
• Experimental temperature profile and simulation
  (ANSYS) profile are similar.
• E values for PMMA drops with temperature.
• E drops substantially after 105 deg C indicating
  the glass transition temperature.

17
Future Work
Polymer behavior

• Williams-Landel-Ferry (WLF) equation
• Time to fill a cavity
• Polymer flow during Embossing

18
Hot Embossing Machine
19
Mini-Vacuum Chamber

• Mini vacuum chamber used to provide a clean and
  moisture free environment during embossing.
• Mini vacuum chamber can accommodate an 8
  substrate.