Hot Embossing Microfabrication

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Hot Embossing Microfabrication
Hot Embossing is a technique of imprinting
microstructures on a substrate (polymer) using a
master mold (silicon tool).
2
Steps in Hot Embossing

• Heating Silicon Polymer above glass transition
  temperature (Tg).
• Applying load by pressing the silicon tool on
  polymer at certain embossing pressure.
• Cooling the silicon tool and polymer assembly
  below Tg and de-embossing the tool.

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Advantages of Hot Embossing System

• Cost effective Easy manufacturability.
• Time efficient Fast process.
• Fabrication of high aspect ratio features.
• Bio-Compatible surfaces Polymer substrates
  used.
• Disposable Low cost for volume production.

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Applications of Hot Embossing

• BioMEMS/Bio-Sensors
• Micro-Fluidic Devices
• Micro-Optics
• m-TAS (Micro Total Analysis Systems)

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Hot Embossing v/s Other MEMS Fabrication
Processes
Characteristics LIGA Surface Micro-machining Hot Embossing
Number of layers 1 3-5 1
Minimum feature size 5 microns 5 microns 1 micron
Aspect ratio 20 N/A 10
Cost High Moderate Low
Productivity Moderate Low High
Residual Stress Very Low High Low
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Product Comparison
Process Parameters Existing Systems Existing Systems Our System
  Jenoptik EV group  
Maximum Substrate Size Ø 6" Ø 8" Ø 8"
Embossing Force lt 200kN 40kN 0 - 200kN
Heating Time lt 7 minutes 6 minutes 3 minutes
Cooling Time lt 7 minutes 5 minutes 2 minutes
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Schematic Representation of Hot Embossing Setup
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Hot Embossing Conceptual Solid Models
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Heating Subsystem Thermal Analysis

• Heating block dimensions and number of cartridges
  found by a parametric study.
• 53 heating cartridges (1 kW, Ø 1/2, 10 long) on
  each heating block of 10 (L) x 10.5 (B) x 4 (H).

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Heating Subsystem Thermal Analysis (Cont..)

• Appropriate zone configuration of heating
  cartridges for
• optimal heating time,
• prevention of hot spots, and
• uniform heating on mold and substrate surfaces.
• 5 heating zones per heating block having
  different heating power/heat flux.

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Heating Subsystem Thermal Analysis (Cont..)

• Zone Configuration obtained using iterative
  transient FEM thermal analysis in ANSYS.
• Transient behavior of heating cartridges also
  taken into account.

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Forcing Subsystem Structural Analysis

• Forcing System used to provide embossing force.
• Forcing provided by a Dual Column Floor Mounted
  Frame material testing system by Instron
  Corporation model 5800.
• Thermal solution incorporated for FEM structural
  analysis.
• Material modeling incorporates Youngs modulus
  and Poissons ratio variation with temperature.

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Forcing Subsystem Structural Analysis (Cont..)

• 1/4th model used for finite element analysis due
  to symmetry.

Displacement contour plot from structural
analysis
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Cooling Subsystem

• 15 Ton (52.76 kW) chiller and Temperature
  Controller used to cool the system within 2
  minutes.
• Cooling plates divided into 5 zones (5 inputs, 5
  outputs) to obtain
• uniform temperature distribution on the mold and
  substrate surfaces.
• optimize cooling time.
• Manifolds and flow-meters used to evenly
  distribute the cooling oil into the cooling
  plates.

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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.

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Control Subsystem

• Compact Fieldpoint system and LabVIEW by National
  Instruments used for data acquisition and control
  of the main system and individual sub-system.

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Control Subsystem (Cont..)

• LabVIEW is used to
• Monitor
• the chiller set-points,
• the temperature across the master and the
  substrate,
• the pressure in the vacuum chamber.
• Control
• the motion (displacement and velocity) of the
  embossing machine,
• the flow of the cooling oil through the cooling
  block,
• the current through the heater cartridges
• relief valve of the vacuum chamber.