Precise Micro Pattern Replication by Hot Embossing

The LIGA (Lithografie, Galvanoformung, Abformung [German: lithography, electroplating, and molding]) process is one of the promising techniques for fabrication of microstructures having high aspect ratios. Microstructures as high as a few hundred µm or more are widely used for various devices, such as micro-actuators, micro-mechanisms, and micro-sensors. The key to reducing the microstructure fabrication cost of the LIGA process is by using micro replication technology. Hot embossing is attracting the attention of engineers as one such technology for economically mass-fabricating microstructures on thin plastic sheets. This technology is especially effective for precisely replicating micro patterns on relatively large sheets. This paper describes the results of research the authors recently carried out to find the optimal conditions for hot embossing in the atmosphere and in a vacuum. For a series of experiments, we prepared two types of Ni molds each containing an area of 33 × 33mm2 distributed with hole or column patterns 60µm in diameter and 1.0 in aspect ratio. The LIGA process using synchrotron radiation fabricated these patterns. From the experiments, we could determine the optimal conditions for replicating these patterns on PMMA sheets in a normal-atmosphere and vacuum environments.