Photo-electroforming: 3-D geometry and materials flexibility in a MEMS fabrication process

Photo-electroforming is a new manufacturing process for making microelectromechanical systems (MEMS). Photo-electroforming builds parts by an additive process which defines geometry by depositing powder in layers and creating regions of selective conductivity by laser-enhanced electroless plating. The conductive region is then joined by a second plating to form an integral part. The unmetallized portion is removed by selective etching in one step after all layers are defined and joined. Single-layer and two-layer stand-alone parts made of nickel/silicon carbide composites of overall size 75-100 μm and feature size 25 μm were created. Writing speeds of up to 24 cm/s and in-plane resolution of 15 μm were demonstrated. The high laser-induced plating rates were found to be due to elevated substrate temperatures under the laser spot and enhanced mass transfer due to pumping by the hydrogen bubbles resulting from the plating reaction. In the regimes studied, mass transfer defined the rate limit. The in-plane resolution was found to be limited by a combination of laser spot size, thermal conduction in the substrate, and laser divergence due to gas bubbles