Long-term creep behavior of SU-8 membranes: Application of the time-stress superposition principle to determine the master creep compliance curve

摘要

We employ the concept of time-stress superposition on short-term creep tests to determine the master creep compliance curve of glassy SU-8. For the determination of the creep curves, the bulge test method is used. Rectangular membranes with a thickness of 2.25 mu m, widths from 830 mu m to 941 mu m and a length of >= 6 mm are fabricated and measured. The chosen geometrical dimensions allow for the assumption of plane strain conditions. SU-8 exhibits rather low creep (<= 10% at t= 10(10) s) under constant equivalent stress of 13.2 MPa, where the initial value Do and transient component D-e of the creep compliance are found to be 0.23 GPa(-1) and 0.29 GPa(-1), respectively. The fracture strength sigma(f) of the fully cured epoxy resin is measured to be 73.3 MPa. We report on modeling, fabrication, error analysis and experimental results. (C) 2007 Elsevier B.V. All rights reserved.