Influence of moisture on humidity sensitive material parameters of microelectronics relevant polymers
It is well known that properties of polymer materials are highly dependent on temperature, time, curing conditions etc. The use of temperature and time dependent material parameters is state-of-the-art in microelectronic packaging. This paper presents various modified measurement methods for analysing the effect of moisture of thermo-mechanical properties of MEMS-relevant polymer systems. In the micro materials-lab, we developed an advanced measurement method - modified DMA multifrequency and hygroscopic swell analysis - for the determination of moisture dependent parameters for micro and nano scale samples. The time-moisture superposition principle has been introduced for some polymers where a humidity shift factor is used along the frequency axis at constant temperature. The relationship between the humidity shift factor and the equilibrium water content is analogically described by the WLF (Williams-Landel-Ferry)-type-equation on the time-temperature superposition. T he main conclusions are that the water molecules seem to weaken the intermolecular forces for the polymers to prefer the state of entropy elasticity already to lower temperature, and the moisture shows influences on the visco elastic properties significantly. Furthermore, diffusion in highly filled epoxies does not follow the conventional Fickian diffusion of polymers. Modified non-Fickian absorption models provide an insight to the rate of initial (Fickian) moisture diffusion in the voids compared to the secondary non-Fickian diffusion, and show a very good agreement with experimental data. In combination with numerical methods, new strategies for life-time evaluation and fatigue of microelectronic packaging, MEMS and NEMS can be addressed.