Ultrasonic micro hot embossing of polymers exemplified by a micro thermal flow sensor

A micro thermal flow sensor fabricated by ultrasonic hot embossing has been developed at KEmikro RWTH Aachen University. Ultrasonic micro hot embossing allows fabrication of polymer micro structures with low investment costs. A polymer film is micro patterned by locally melting with ultrasound and molding from a master tool. The entire process is completed in 1-2 seconds. Micro structures with feature sizes of down to 5 micrometer were produced this way at 35 kHz. With the same machine a micro channel was sealed with a special designed tool. The fabrication process is demonstrated by manufacturing a micro thermal flow sensor by ultrasonic hot embossing and welding. The flow sensor consists of a 100 micrometer high, 500 micrometer wide, and 1 cm long channel from polypropylene (PP) which is crossed by a gold wire with a diameter of 50 micrometer. For measurements with water the wire of the sensor was heated up by 15 deg C. The respond time of the sensor was measured to be 24 ms.