M. Heckele, A. Durand

Plastic replication has several advantages for the mass production of components in microsystems. The wide range of properties of polymers allows an optimal fit to the requested application by selection from a great variety of plastic materials. Cost-effective fabrication as one of the main characteristics of the polymer replication offers an access to new applications as single-use devices.

For very high structures, high aspect ratios, structures with thin and long walls or large microstructured areas the vacuum hot embossing process with its high replication quality is well suited.

In this vacuum hot embossing process a microstructured tool, a mould insert, is pressed into a thermoplastic film, heated above its glass-transition temperature. Compared to the injection moulding process, where a closed tool is filled through the gate, in the hot embossing process always remains a non-structured residual layer. This residual layer restricted the hot embossing process up to now to surface structuring. A lot of applications in microsystem technologies, especially in microfluidics require through-holes to connect front and back side of a device.

The technique presented in this paper works with a sandwich film of two different plastic materials. Handling and demoulding is similar to the process with a single layer film. But during the hot embossing process only the upper film is penetrated completely, in this way after separation of the two components the upper film is structured with through-holes.

This technique requires a precise control of the process and optimal material selection for useful layer and residual layer, to maintain the sandwich state during the process and to enable a subsequent separation of the two layers.

In this paper we present a combination of cellulose acetate (AC) and polyoxymethylene (POM) which can be separated after structuring by application of mechanical load. As example we have realized a 100 µm thick micro riddle with a 300 x 300 µm²- mesh separated by 40µm walls.

Other use of this technique is the possibility to realize diced microstructures magazined on a carrier layer.