Cationic electron-beam curing of a high-functionality epoxy: Effect of post-curing on glass transition and conversion

This paper reports on the cationic electron-beam curing of a high-functionality SU8 epoxy resin, which is extensively used as a UV-curing negative photoresist for micro-electronics machine systems (MEMS) applications. Results show that elevated post-curing treatment significantly increased both the conversion and the glass transition. The degree of conversion and the glass transition temperature were measured by using Fourier-transform infrared (FTIR) spectroscopy and modulated differential scanning calorimetry (MDSC®), respectively. The glass transition temperature (T_g), which has been observed to be dependent on the degree of conversion, reaches a maximum of 162°C at 50 Mrad and post-curing at 90°C. The degradation pattern of the cured resin does not show much variation for exposure at 5 Mrad, but does show significant variation for 50 Mrad exposure at various post-curing temperatures. A degree of conversion of more than 0.8 was achieved at a dosage of 30 Mrad with post curing at 80°C, for the epoxy resin with an average functionality of 8 a feature simply not achievable when using UV-curing. © 2004 Society of Chemical Industry.