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..)