Analysis and characterization of demolding of hot embossed polymer microstructures

Micro-molding techniques including injection molding and hot embossing have great potential for manufacturing microfluidic 'lab-on-a-chip' devices for point-of-care diagnostics and many other applications; however, separating the part from the mold (demolding) can pose problems. This paper presents a study of demolding of hot embossed polymer microstructures, including theoretical analysis and finite element simulations, along with demolding experiments using a newly developed test method. Using this method, the energy dissipated during demolding (the demolding toughness) can be determined for individual microstructures. It has been found that both adhesion and sidewall friction play a role in demolding, with adhesion being degraded by thermal stress and friction being exacerbated as the part cools. A minimum value of demolding toughness occurs at the temperature where adhesion is fully degraded. This temperature depends on the initial adhesion strength, the part's material properties and the geometry of mold features. The minimum toughness temperature has been identified for several simple mold patterns for parts made of poly-methyl-methacrylate and polycarbonate. The minimum toughness temperature is higher for sparser patterns of features and lower for denser ones. Below this temperature, the demolding toughness is related to feature height but is not related to feature width.

[1]  Werner Karl Schomburg,et al.  Large-scale hot embossing , 2005 .

[2]  K. Johnson.  Contact Mechanics: Frontmatter , 1985 .

[3]  Hayden Taylor,et al.  HIGH-TEMPERATURE DE-MOLDING FOR CYCLE TIME REDUCTION IN HOT EMBOSSING , 2007 .

[4]  Aaron D. Mazzeo,et al.  Production of Micro-Molding Tooling by Hot Embossing , 2007 .

[5]  Yangchao Tian,et al.  Analysis of the demolding forces during hot embossing , 2007 .

[6]  B. Gross,et al.  Stress intensity factors for crackline-loaded edge-crack specimens. , 1967 .

[7]  Kristen L. Helton,et al.  Microfluidic Overview of Global Health Issues Microfluidic Diagnostic Technologies for Global Public Health , 2006 .

[8]  David E. Hardt,et al.  Replication performance of Si-N-DLC-coated Si micro-molds in micro-hot-embossing , 2010 .

[9]  Yangchao Tian,et al.  Study of Hot Embossing Using Nickel and Ni–PTFE LIGA Mold Inserts , 2007, Journal of Microelectromechanical Systems.

[10]  Lallit Anand,et al.  A thermo-mechanically-coupled large-deformation theory for amorphous polymers in a temperature range which spans their glass transition , 2010 .

[11]  K. K. Kabanemi,et al.  Modeling of large area hot embossing , 2008, ArXiv.

[12]  Peter P. Gillis,et al.  Double‐Cantilever Cleavage Mode of Crack Propagation , 1964 .

[13]  Matthew E Dirckx.  Demolding of hot embossed polymer microstructures , 2010 .

[14]  Fuqian Yang and,et al.  Adhesion of a Rigid Punch to an Incompressible Elastic Film , 2001 .

[15]  Byoung Hee You,et al.  Simulation study on stress and deformation of polymeric patterns during the demolding process in thermal imprint lithography , 2008 .

[16]  A. A. Griffith.  The Phenomena of Rupture and Flow in Solids , 1921 .

[17]  Yangchao Tian,et al.  Study of the demolding process—implications for thermal stress, adhesion and friction control , 2006 .

[18]  Anthony G. Evans,et al.  Decohesion of Thin Films From Ceramic Substrates , 1985 .

[19]  Jaejong Lee,et al.  Demolding temperature in thermal nanoimprint lithography , 2009 .

[20]  M. Worgull,et al.  New aspects of simulation in hot embossing , 2003, DTIP 2003.

[21]  M. F. Kanninen,et al.  An augmented double cantilever beam model for studying crack propagation and arrest , 1973, International Journal of Fracture.

[22]  Helmut Schift,et al.  Measurement of demolding forces in full wafer thermal nanoimprint , 2008 .

[23]  J. Williams,et al.  Corrections needed in double-cantilever beam tests for assessing the interlaminar failure of fibre-composites , 1989 .

[24]  Lallit Anand,et al.  A thermo-mechanically coupled theory for large deformations of amorphous polymers. Part II: Applications , 2011 .

[25]  Mary B. Chan-Park,et al.  Numerical analyses of peel demolding for UV embossing of high aspect ratio micro-patterning , 2009 .

[26]  G. Liu,et al.  The lifetime comparison of Ni and Ni-PTFE moulding inserts with high aspect-ratio structure , 2005 .

[27]  Holger Becker,et al.  Polymer microfabrication technologies for microfluidic systems , 2008, Analytical and bioanalytical chemistry.

[28]  H. Schift.  Nanoimprint lithography: An old story in modern times? A review , 2008 .