A MICROVALVE SYSTEM FABRICATED BY THERMOPLASTIC MOLDING

A process for the fabrication of microvalve systems by thermoplastic m olding and membrane techniques has been developed. The valve system co nsists of three individual valves formed by two parts molded from poly methylmethacrylate PMMA and a polyimide membrane. The mold inserts wer e manufactured by milling of a brass substrate using a 300 mu m diamet er head. The three-dimensional microstructure of the inserts consists of four different levels for valve seats, orifices, alignment pins and cavities. The overall diameter and height of the whole valve system i s 7 mm and 1.9 mm, respectively. The valves are designed to be normall y open. To close the valves, the pressure in an actuator chamber above the membrane is raised by a heater coil and the membrane is pressed o nto the valve seat. First measurements at a difference pressure of 100 0 hPa showed a rate of water flow through a single valve of 171 mu ls( -1). An actuator pressure of 180 hPa was reached by heating air with a resistive heater and continuous electrical power of 158 mW. A valve s upplied with nitrogen at 130 hPa was closed by an electrical power of 116 mW.