Hot micro-embossing of thermoplastic elastomers

Abstract

Microfluidic devices have been a rapidly increasing area of study since the mid 1990s. Such devices are useful for a wide variety of biological applications and offer the possibility for large scale integration of fluidic chips, similar to that of electrical circuits. With this in mind, the future market for microfluidic devices will certainly thrive, and a means of mass production will be necessary. However PDMS, the current material used to fabricate the flexible active elements central to many microfluidic chips, imposes a limit to the production rate due to the curing process used to fabricate devices. Thermoplastic elastomers (TPEs) provide a potential alternative to PDMS. Soft and rubbery at room temperature, TPEs become molten when heated and can be processed using traditional thermoplastic fabrication techniques such as injection molding or casting. One promising fabrication technique for TPEs is hot micro-embossing (HME) in which a material is heated above its glass transition temperature and imprinted with a micromachined tool, replicating the negative of the tools features. Thus far, little research has been conducted on the topic of hot embossing TPEs, and investigations seeking to determine ideal processing conditions are non-existent. This investigation concerns the selection of a promising TPE for fabrication of flexible active elements, and the characterization of the processing window for hot embossing this TPE using a tool designed to form long winding channels, with feature heights of 66Cpm and widths of 80jpm. Ideal processing conditions for the tool were found to be pressures in the range of 1MPa-1.5MPa and temperatures above 1400.

(cont.) The best replication occurred at 1500 C and 1.5 MPa, and at these conditions channel depth was within 5% of the tool, and width was within 10%. For some processing conditions a smearing effect due to bulk material flow was observed. No upper limit on temperature was found, suggesting that fabrication processes in which the material is fully melted may also be suitable for fabrication of devices from TPEs.