| 초록 |
Polyimides have been used in many applications for their excellent thermal, mechanical, and electrical properties. For example, they can be used as insulation layers for semiconductor devices or substrates for flexible printed circuits. In multilevel interconnection packaging, polyimides seem to be very good candidates as dielectric materials. One of the major concerns about the use of polyimide films is dimensional stability. Sometimes high stress is generated at the interfaces by the mismatch between physical properties of the interfaced layers, and this may result in reliability problems such as displacement, crack, and delamination. Therefore, the matching of these properties for the interfaced layers is necessary to minimize the generation of interfacial stress. The Poisson’s ratio generally varies in the range of 0.2-0.5, depending on the materials including metals, ceramics, and polymers. The TEC of a polymer film is strongly dependent upon the polymer chain rigidity as well as the molecular orientation. And the stress at polyimide thin film on a substrate can be minimized by controlling the TEC of the polymer through the modification of the polymer backbone and the control of molecular orientation. The molecular orientation of polyimide thin film is affected by film thicknesses and moisture uptake and changes the residual stress. So it is much important to investigate the relationship between film thickness and residual stress or between moisture uptake and the relaxation of residual stress. In this work, we have investigated the effect of film thickness and moisture uptake on the residual stress of poly(oxidiphenylene pyromellitimide)(PMDA-ODA) using a computer-controlled thin film stress measurement system(TFSMS). First, we measure the residual stresses generated during thermal cycling depending on film thicknesses. Then, for each thickness the relaxation of residual stress is measured at 25C.
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