Hot embossing as a method for rapid prototyping microfluidic devices

Abstract

Hot embossing is a growing technology proven to be capable of reproducing micro-scale features on thermoplastics and can be an effective process for rapid prototyping microfluidic devices with high aspect ratio micro features. Advantages of this manufacturing process can include tooling flexibility, fast production time, low capital cost and a vast selection of production materials. A greater understanding on the micro feature transferring capabilities and use limits of tools are needed so that hot embossing may advance to becoming a practical technique for producing microfluidic parts. This work focuses on both the design and analysis of a hot embossing system and a brass tool to replicate an existing functional high aspect ratio micro feature onto Polymethyl methacrylate (PMMA). The aspect ratio of features ranged from 10:1 to 4,000:1. Optimal embossing parameters used a pressure of 3.5kN, hold time of 12 minutes, tool temperatures of 140°C and substrate temperature of 130°C to produce parts that filled shoulder heights and widths up to 97% and 90%, respectively. The wearing of features on the metal tool were also characterized for purposes of understanding the limits on tool use and was found that a maximum range of +/-3[mu]m in dimensional change existed. Gains in tool dimensions were then mainly attributed to the deposition of embossed materials onto the tool. The study further determined a method for creating usable resin tool copies that exhibited a replication accuracy of less than 2%, on average, for micron size features.