Development of Bulge Testing System for Mechanical Properties Measurement of Thin Films : Elastic Modulus of Electrolytic Copper Film

박막의 기계적 물성 측정을 위한 벌지 시험 시스템 개발: 전해 동 박의 탄성 계수

A bulge testing system was developed to measure mechanical properties of thin film materials. A bulge pressure test system for pressurizing the bulge window of the film and a micro out-of-plane ESPI(Electronic Speckle Pattern Interferometric) system for measuring deflection of the film were included in the testing system developed. For the out-of-plane ESPI system, whole field speckle fringe pattern, corresponding to the out-of-plane deflection of the bulged film, was 3-dimensionally visualized using 4-bucket phase shifting algorithm and least square phase unwrapping algorithm. The bulge pressure for loading and unloading was controlled at a constant rate. From the pressure-deflection curve measured by this testing system, ain-plane stress-strain curve could be determined. In this study, elastic modulus of an electrolytic copper film 18 ${\mu}m$ was determined. The modulus was calculated from determining the plain-strain biaxial elastic modulus at the respective unloading slopes of the stress-strain curve and for the Poisson's ratio of 0.34.