Hot embossing on polymethyl methacrylate

Abstract

Micro hot embossing experiments were conducted on polymethyl methacrylate (PMMA) to look at the effects of holding load, temperature and time on the fidelity of line arrays representing micro channels. The results revealed that the holding temperature was a more sensitive parameter than the others due to its large effect on the polymer's viscoelastic properties. Large variations in the channels' imprinted widths and depths could be seen when the holding temperature was spanned over the glass transition range of PMMA. Dynamic mechanical analysis (DMA) on PMMA revealed a steep glass transition over a 20degC range, with the material losing more than 95 % of its storage modulus, E'. The loss modulus, E" peaked at 108degC for the 0.1 Hz frequency sweep and tan 5 peaked well above 1.2. The data explained why large variations in the channels' imprinted widths and depths could be seen when the holding temperature was spanned over the glass transition range of PMMA. Experimental investigations on holding and cooling effects revealed 3 regions of process stability. The region in the glass transition range was highly unpredictable due to the sensitivity of the E' to slight changes in the temperature distribution. The embossed features were non uniform in this region - showing different degrees of imprinted depth within the line array. This phenomenon was not seen in the typical hot embossing process where the holding time and cooling time were not at zero. Cooling effect plots showed substantial polymer movement with the maximum embossed depth achieved with demoulding at just 10degC below the holding temperature