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Abstract

Various techniques for the fabrication of highly accurate master molds with precisely defined microstructures for use in plastic replication using injection molding, hot embossing, or casting techniques are disclosed herein. Three different fabrication processes used for master mold fabrication are disclosed wherein one of the processes is a combination of the other two processes. In an embodiment of the first process, a two-step electroplating approach is used wherein one of the metals forms the microstructures and the second metal is used as a sacrificial support layer. Following electroplating, the exact height of the microstructures is defined using a chemical mechanical polishing process. In an embodiment of the second process, a modified electroforming process is used for master mold fabrication. The specific modifications include the use of Nickel-Iron (80:20) as a structural component of the master mold, and the use of a higher saccharin concentration in the electroplating bath to reduce tensile stress during plating and electroforming on the top as well as sides of the dummy substrate to prevent peel off of the electroform. The electroforming process is also well suited towards the fabrication of microstructures with non-rectangular cross sectional profiles. Also disclosed is an embodiment of a simple fabrication process using direct deposition of a curable liquid molding material combined with the electroforming process. Finally, an embodiment of a third fabrication process combines the meritorious features of the first two approaches and is used to fabricate a master mold using a combination of the two-step electroplating plus chemical mechanical polishing approach and the electroforming approach to fabricate highly accurate master molds with precisely defined microstructures. The microstructures are an integral part of the master mold and hence the master mold is more robust and well suited for high volume production of plastic MEMS devices through replication techniques such as injection molding.

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First Claim