Micromolding of biochip devices designed with microchannels

Microfabrications of polymer are becoming increasingly important and considered as a low-cost alternative to the silicon or glass-based Micro-Electro-Mechanical System (MEMS) technologies. In this study, micromolding via both microinjection molding and hot embossing were applied to microfeatured fluidic platform used for DNA/RNA test. LIGA like processes were used to prepare silicon-based SU-8 photoresist followed by electroforming for making Ni-Co based stamp. The microfeature in the stamp consists of microchannel array of approximately 27 mu m in depth and 110 mu m in width. A polymethyl methacrylate (PMMA) film of 1 mm thickness was used as a hot embossing substrate and PMMA resin was also used as the injection molding material. Effect of various molding conditions on the replication accuracy of microfeatures was investigated. The width and depth of microchannels within molded devices were measured and analyzed. For hot embossed device, it was found that applied pressure and embossing temperature are the two key parameters affecting molding accuracy significantly. The accuracies of the imprint width and depth increased with the applied pressure until the associated dimensions reached saturated values. Embossing temperature shows similar influence on the accuracies of imprint depth and width as the applied pressure. As for microinjection molded devices, the accuracies of the imprint width and depth increased with increasing mold temperature, melt temperature, injection velocity and packing pressure within regular processing window. Basically, both micromoldings can achieve the molding accuracies requirement for microchannels. Compared with hot embossing, microinjection molding shows a slight advantage in the replication of depth of microchannel but is poor in width. The cycle time of hot embossing is significantly longer than that of microinjection molding. (c) 2006 Elsevier B.V. All rights reserved.