Investigations on Transport Phenomena Governing Replication of Electroforming Micromolds for Fabrication of High Aspect Ratio Microstructures

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CTS-0651752: INVESTIGATIONS ON TRANSPORT PHENOMENA GOVERNING REPLICATION OF ELECTROFORMING MICROMOLDS FOR FABRICATION OF HIGH ASPECT RATIO MICROSTRUCTURES; PI: PITCHUMANIPROJECT ABSTRACTFabrication of microstructures has been the subject of considerable attention in recent years. While techniques such as surface silicon micromachining and bulk silicon etch are used as practical methods for thin microstructures, processes such as LIGA (an acronym for the German words for lithography, electrodeposition, and molding) offer the capability to fabricate high aspect ratio microstructures (HARMs). A drawback of LIGA-based fabrication, however, is the need for repeated synchrotron exposure and development steps, which are both expensive and time-consuming. Commercial viability of the LIGA process requires economical replication technologies to eliminate the repetitive synchrotron exposure and development steps.INTELLECTUAL MERIT: Responding to the above-mentioned need, proposed is a collaborative investigation with Sandia National Laboratories on a new technique for rapid replication of electroforming micromolds with integral microscreens. The process is based on injection molding or hot embossing of plastic replicates with integral metallic screens onto a LIGA-fabricated master microtool, to produce sacrificial electroforming molds in which the metallic screen acts as the conducting base and the plastic features provide insulating sidewalls for electrodeposition of the desired metallic micropart. Since many plastic replicates of the electroforming molds could be produced rapidly from a single LIGA-fabricated microstamp base, the need for repetitive synchrotron exposure and development is obviated, thus resulting in an economical and commercial advantage. Proposed is a balanced computational and experimental study on the transport phenomena governing the fabrication process, to systematically investigate the effects of the various process, material, and geometric parameters. A comprehensive processing-to-part simulation capability will be developed, which will be used to investigate the competing effects of the phenomena governing the process and, in turn, to derive optimum process and material designs. Experimental studies will focus on (a) characterization of microscale polymer rheology of the materials considered to provide the needed fundamental information in the modeling; and (b) several systematic processing runs to validate the computational models and to demonstrate the optimum regimes identified from the modeling. The proposed program will have a significant technological impact in the MEMS industry through the development of capabilities for rapid and cost-effective fabrication of microparts.BROADER IMPACT: The program will have significant educational impact by training two graduate students in an important field of much technological relevance. The students will gain valuable experience through internships and close interactions with researchers at Sandia during the program. Efforts will be made to recruit one or both students who are either women or from other underrepresented groups, which will broaden the societal impact.