Post on 17-Dec-2015
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 Femto-
Second Laser
Heat the substrate and mold to justabove Tg of the
substrate
Apply embossingforce on the
substrate via themold under vacuum
Cool the substrate
and mold to just below Tg
De-embossingof 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
-TAS (Micro Total Analysis Systems)
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
Process Parameters Existing Systems Our System
Jenoptik EV group
Maximum Substrate Size Ø 6" Ø 8" Ø 8"
Embossing Force < 200kN 40kN 0 - 200kN
Heating Time < 7 minutes 6 minutes ~ 3 minutes
Cooling Time < 7 minutes 5 minutes ~ 2 minutes
Product Comparison
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
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.
Temperature Uniformity at the Mold and Substrate Surface
199.5
200
200.5
201
201.5
202
202.5
203
0 2 4 6 8 10 12Width of Heating Block (Inches)
Heating Subsystem: Thermal Analysis (Cont..)
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.
Displacement Profile at the Mold Surface
-30
-25
-20
-15
-10
-5
0
5
0 1 2 3 4 5 6
Width (Inches)
Dis
plac
emen
t (M
icro
ns)
Displacement contour plot from structural analysis
1/4th model used for finite element analysis due to symmetry.
Forcing Subsystem: Structural Analysis (Cont..)
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.
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.
Control Subsystem (Cont..)