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 (T g ). Applying load by pressing the silicon tool on polymer at certain embossing pressure. Cooling the silicon tool and polymer assembly below T g and de-embossing the tool. Master/Mold from Femto- Second Laser Heat the substrate and mold to just above T g of the substrate Apply embossing force on the substrate via the mold under vacuum Cool the substrate and mold to just below T g 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  -TAS (Micro Total Analysis Systems)

Hot Embossing v/s Other MEMS Fabrication Processes CharacteristicsLIGASurface Micro- machining Hot Embossing Number of layers13-51 Minimum feature size5 microns 1 micron Aspect ratio20N/A10 CostHighModerateLow ProductivityModerateLowHigh Residual StressVery LowHighLow

Process ParametersExisting SystemsOur System JenoptikEV group Maximum Substrate SizeØ 6"Ø 8" Embossing Force< 200kN40kN kN Heating Time< 7 minutes6 minutes~ 3 minutes Cooling Time< 7 minutes5 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 thicknessParametric 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. 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 Thermal solution incorporated for FEM structural analysis. Material modeling incorporates Young’s modulus and Poisson’s ratio variation with temperature.

Displacement contour plot from structural analysis 1/4 th 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..)