No abstract

Demand has increased for the double-sided moulding of microfluidic devices for a series of biochemical analyses. Accurate alignment of mould inserts is a critical aspect to transfer doubled-sided patterns on the top and bottom surfaces of a moulded part. A method of mould alignment was studied for double-sided hot embossing of polymer microfluidic devices. An alignment method was designed using kinematic constraints, and a set of three locating pins. To validate the alignment method, two brass mould inserts with fluidic reservoirs were used for the double-sided moulding of prototype microfluidic devices. The kinematic constraints were used to align the mould inserts with each other on the hot embossing machine. The misalignment of double-sided features on the moulded parts was measured using a measuring microscope. The X-and Y-magnitudes of the mismatches ranged from −28 to 118 µm along the X-axis of the moulded parts. The X-and Y-magnitudes of the mismatches along the Y-axis of the moulded parts varied from −38 to 141 µm. The results of the experiments showed that the mould alignment using kinematic constraints is applicable to the fabrication of double-sided patterns for microfluidic devices.

The flow behavior of polymers was analyzed using a commercial finite element software, DEFORM-2D, for the replication of microstructures. An alignment structure for microassembly, a hemisphere-tipped post, was modeled to demonstrate the polymer flow in hot embossing. The mold filling with polymer was evaluated by the heights of molded posts. The results of simulation showed better replication fidelity of the post with the increase of the molding temperature and displacement of the mold insert. The complete filling of a mold cavity was achieved at the molding temperatures of 112.5, 125, 137.5, and 150°C when the displacements were 1.5, 2.0 and 2.5 mm. The model can be used to design the process parameters for the reliable replication of microstructures.