Neural network approach to modeling hot intrusion process for micromold fabrication Pun Pang Shiu a , George K. Knopf a , Mile Ostojic b , and Suwas Nikumb b a Dept. of Mechanical & Materials Eng., The University of Western Ontario, London, Ontario, Canada b Industrial Materials Institute, National Research Council Canada, London, Ontario, Canada ABSTRACT The rapid fabrication of polymeric mold masters by laser micromachining and hot-intrusion permits the low cost manufacture of microfluidic devices with near optical quality surface finishes. A metallic hot intrusion mask with the desired microfeatures is first machined by laser and then used to produce the mold master by pressing the mask onto a polymethylmethacrylate (PMMA) substrate under applied heat and pressure. A thorough understanding of the physical phenomenon is required to produce features with high dimensional accuracy. A neural network approach to modeling the relationship among microchannel height (H), width (W), the intrusion process parameters of pressure and temperature is described in this paper. Experimentally acquired data are used to both train and test the neural network for parameter- selection. Analysis of the preliminary results shows that the modeling methodology can predict suitable parameters within 6% error. Keywords: microfluidic devices; neural network modeling; micromold fabrication 1. INTRODUCTION Microfluidic devices, analytical microsystems, and lab-on-a-chip (LOC) technologies have greatly advanced diagnostic medicine in recent years. These microsystems significantly increase the speed of analysis and lower the cost in performing the tests because of the small amount of reagents consumed during analysis. However, these miniature devices must be disposable in order to avoid sample contamination. It is, therefore, necessary to incorporate cost effective methods of volume production for designing and developing microfluidic devices. The methods of volume production for polymer-based microfluidic devices have been explored previously, such as hot embossing 1,2 , and microinjection molding 3,4 . These volume production methods are replication technologies that require mold masters, which are typically expensive to fabricate. The well-recognized methods for fabrication of mold masters of microfluidic devices are the LIGA (lithography, galvano-forming and plastic molding) and Soft-lithography technique. The LIGA method produces microfeatures of mold masters with high quality of surface finishes as well as high aspect ratio structures. The process employed X-ray lithography to transfer microchannel patterns onto PMMA resist. The resulting PMMA microstructures are then electroplated. The limitation of the LIGA method is its high-cost of the process 5,6 . Soft-lithography 7-10 is another popular method to fabricate mold masters. These mold masters are used to replicate polydimethylsiloxane (PDMS) elastomer based microfluidic devices. The microchannel patterns are transferred via UV-lithography technique. The advantage of the method is that UV-lithography systems are widely available. This fabrication method requires a number of steps to produce the mold masters 8 . Both fabrication methods are based on lithography technique. Shui et al. 11 reported a non-lithography-based method that fabricates metallic mold masters for replication of PDMS- based microfluidic devices. The method involves laser cutting of microchannel features from a thin metallic sheet (50 to 75µm thick) and the mcirochannel features were then laser welded onto a metal substrate to form the final mold masters. A Y-channel microfluidic mixer fabricated via this method was demonstrated 11 . The advantages of this method to fabricate mold masters are that it only involves a few fabrication steps, laser cutting and welding. The LHEM (Laser micromachining, partial Hot Embossing, and Molding) method is another non-lithography-based mold master fabrication method 12 . The advantage of the method is that the microchannel features of mold masters have near optical surface finishes. The method involves laser micromachining and hot intrusion (partial hot embossing) process. Subsequently, the mold masters were used to replicate PDMS-based microfluidic devices. To design microfludiic Optomechatronic Technologies 2008, Otani, Bellouard, Wen, Hodko, Katagiri, Kassegne, Kofman, Kaneko, Perez, Coquin, Kaynak, Cho, Fukuda, Yi, Janabi-Sharifi, Eds., Proc. of SPIE Vol. 7266, 72661V • © 2008 SPIE • CCC code: 0277-786X/08/$18 • doi: 10.1117/12.817359 Proc. of SPIE Vol. 7266 72661V-1 2008 SPIE Digital Library -- Subscriber Archive Copy