Hot Embossing
Microfabrication
Hot Embossing is a technique of
imprinting microstructures on a
substrate (polymer) using a master
mold (silicon tool).
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.
Master/Mold
from FemtoSecond Laser
Heat the substrate
and mold to just
above Tg of the
substrate
Apply embossing
force on the
substrate via the
mold under vacuum
Cool the
substrate
and mold to just
below Tg
De-embossing
of the mold and
substrate
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.
Applications of Hot Embossing

BioMEMS/Bio-Sensors

Micro-Fluidic Devices

Micro-Optics

m-TAS (Micro Total Analysis Systems)
Hot Embossing v/s Other
MEMS Fabrication Processes
Characteristics
Number of layers
LIGA
Surface MicroHot
machining
Embossing
1
3-5
1
5 microns
5 microns
1 micron
20
N/A
10
High
Moderate
Low
Productivity
Moderate
Low
High
Residual Stress
Very Low
High
Low
Minimum feature size
Aspect ratio
Cost
Product Comparison
Process Parameters
Maximum Substrate Size
Embossing Force
Existing Systems
Our System
Jenoptik
EV group
Ø 6"
Ø 8"
Ø 8"
< 200kN
40kN
0 - 200kN
Heating Time
< 7 minutes 6 minutes
~ 3 minutes
Cooling Time
< 7 minutes 5 minutes
~ 2 minutes
Schematic Representation of
Hot Embossing Setup
Hot Embossing Conceptual
Solid Models
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).
Parametric study to determine heating block thickness
Parametric study to determine number of cartridges
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.
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.
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 Young’s modulus
and Poisson’s ratio variation with temperature.
Forcing Subsystem: Structural
Analysis (Cont..)

1/4th model used for finite element analysis
due to symmetry.
Displacement Profile at the Mold Surface
Displacement (Microns)
5
0
-5 0
1
2
3
4
5
6
-10
-15
-20
-25
-30
Width (Inches)
Displacement contour plot from
structural analysis
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.
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.
Control Subsystem

Compact Fieldpoint system and LabVIEW by
National Instruments used for data acquisition
and control of the main system and individual
sub-system.
Control Subsystem (Cont..)

LabVIEW is used to:

Monitor

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the chiller set-points,
the temperature across the master and the substrate,
the pressure in the vacuum chamber.
Control

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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.