Electrochemically based low-cost high precision processing in MOEMS packaging

Precision processing in MOEMS (micro-opto-electromechanical systems) packaging has been studied based on electrochemical processes with the purpose of establishing technology for low-cost multifunctional encapsulation of microsystems and assembly of opto-electric access links in polymer. The electrochemically based processes studied in this paper include: 1. Electroforming of a polymer moulding tool (stamper) in a nickel sulphamate electrolyte on a high-precision 3D etched silicon template. 2. Patterning of 3D surfaces by an electrophoretic photoresist. 3. Precision plating of Au and Sn for self-alignment of chips by eutectic Au–Sn solder. The results show that nickel stampers with adequately low internal stress can be electroformed on 3D silicon wafers. Furthermore, 3D polymer samples manufactured by the nickel stampers can be patterned with metal lines down to 20 μm width using electrophoretic photoresist. Finally, eutectic Au–Sn solder bumps are realized by electroplating of Au and Sn followed by reflowing, satisfying the demands on dimension and alloy composition control over a 4 in. Si wafer.