Prüfstand zur Charakterisierung der Gas-Leckrate von Silizium-Mikroventilen

Micropumps and microvalves are used to control the movement of fluids. One problem with silicon microvalves is the unwanted backflow of fluids in the reverse direction, the so-called leakage rate. Many applications require that they do not have high leakage rates, which causes problems in vacuum applications, for example. The cause for the leakage rate of silicon microvalves is the roughness of the surface of the valve flap and the support bridge, the bending of the valve flap when pressurized in the reverse direction, and the initial gap caused by the manufacturing process. In this work, a semi automated, universal test bench for characterizing the gas leakage rates of silicon microvalves is designed and fabricated. In the concept phase, various leakage tests are considered and a FMEA is performed to find the most suitable measurement method for the leakage rates of silicon microvalves. The result of the analysis is the differential pressure measurement with overpressure. This measurement method is convincing due to few components, low error rate and the possibility to measure leakage rates smaller than 0,01 cm3/min via the pressure drop and a known volume. The test bench consists of a pressure transmitter, a housing for the test valves, a pressure chamber and a high-resolution pressure sensor. To validate the measurements, several leak tests are performed on the individual components of the test bench. In addition, the test bench is compared with a conventional flow measurement. This demonstrates the advantage of the differential pressure measurement with overpressure, which allows accurate calculation of the leak rate by directly measuring the pressure decay and therefore has no problems with dead volumes or low volume flow rates. In addition, characteristics are presented for leakage rates to be expected when measuring the finished test valves on the test bench, such as the duration of the pressure measurement, the magnitude of the volume flows at certain times and the influence of the initial gap. Overall, the test bench provides good results that are in the same order of magnitude as theory and allows the characterization of the leakage rates of different variants of silicon microvalves.