SIMTech technical reports (STR_V8_N3_09_MDM) Volume 8 Number 3 Jul-Sep 2007 174 Hot embossing on polymethyl methacrylate S. H. Ng, and Z. F. Wang Abstract – This report is a parametric study on the hot embossing of polymethyl methacrylate (PMMA). The work is performed to understand the influence of the various process parameters on the embossed micro size patterns with the aim to develop the capability for microfluidic devices manufacturing. Experimental result reveals that the holding temperature shows significant effect, especially near the glass transition temperature (T g ) of the PMMA. In addition, the cooling phase of the process also showed the occur- rence of significant polymer flow. Keywords: Polymethyl methacrylate, Hot embossing, Microfluidics 1 BACKGROUND As the demand for low cost and disposable mi- crofluidic devices increases, there is a need for a fab- rication process that is both low cost and capable of mass production. The earlier devices are mostly made of silicon, silicon oxide or glass partly due to the adoption of the MEMS fabrication processes. How- ever, cost is an issue and the process is not suitable for mass production. In overcoming these issues, polymer will be the preferred choice due to its low material cost and the scalable manufacturing processes associated with it. Polymethyl methacrylate (PMMA) is a common and low cost polymer material. It has been reported as the least hydrophobic of common plastic materials [1,2]. Moreover, its optical clarity is also a significant benefit. One of the fabrication methods for PMMA mi- crofluidic devices is the hot embossing process where the structures of a master mould are copied onto the PMMA sample. The process offers low cost and ease of mass production [2-5]. In this paper, we present the results of an investigation on the PMMA behaviour during the hot embossing process. 2 OBJECTIVE The objective of this work is to study the behav- iour of the PMMA material hot embossing process, with the aim of providing an optimised manufacturing process for microfluidic devices. Two sets of experiments were performed. The first experiments consisted of an investigation of the effect of three identified parameters, namely: load, temperature, and time. The second set of experiments consisted of investigation of the holding phase and the cooling phase of the hot embossing process. 3 METHODOLOGY Hot embossing was conducted on 1 mm thick PMMA sheets using a hybrid stamp based on the FR4 printed circuit board material. The hybrid stamp con- sisted of a 1.6 mm thick FR4 glass fibre reinforced epoxy topped with a 34 μm layer of copper. A pattern of raised structures from one of these copper surfaces was created by nickel electrolytic plating. The stamp used in the experiments was measured to be 55 mm x 48 mm x 1.6 mm. The equipment was a bench-top hydraulic press with a capacity of 15 tons load. It was fitted with two 100 mm diameter heated platens (top and bottom) and these were connected to a temperature controller. A thermocouple was embedded into one of the platens. Cooling was achieved through the air and water cooled plates attached to the platens. Figure 1 shows the hot embossing system. Fig. 1. The hot embossing system. The procedure for the hot embossing process was as follows (see Fig. 2): 1. Load the sample 2. Heat to the holding temperature 3. Apply the holding load 4. Hold the load and temperature for a certain amount of time (the holding time) 5. While still holding the load, cool to ~ 90ºC 6. Remove the load 7. Remove the sample Pressure gauge Platen Pumping lever