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Passive micro-assembly of modular, hot embossed, polymer microfluidic devices using exact constraint design

Low-cost microfluidic platforms have the potential to change accepted practices in many fields, including biology and medicine, in the near future. Micro-assembly of molded polymer microfluidic devices is one approach to cost-effective mass production of modular, microfluidic instruments. Polymer, passive alignment structures were used to precisely assemble molded polymer components to prevent infinitesimal motions and minimize the misalignment between assembled components and devices. The motion and constraint of the assemblies were analyzed using screw theory to identify combinations of passive alignment structures that would provide exact constraint of all degrees of freedom of the two mating parts without over-constraint. One option identified by kinematic analysis was a set of three v-groove and hemisphere-tipped pin joints, which are well known from precision engineering and suitable for microfabrication. To validate the passive alignment scheme, brass mold inserts containing alignment structures were micro-milled and used to hot emboss components in polycarbonate (PC). Dimensional and location variations of prototype alignment structures were measured to quantify the difference between the as-designed and actual dimensions and the locations of the alignment structures. The dimensional variation was 0.2–3% less than the designed dimensions and the location variation was 0.7% less. The alignment accuracy of an assembly was characterized by measuring the mismatch and vertical variation between molded alignment standards embossed on each pair of mating plates. With molded, polymer alignment structures the mean mismatch and mean vertical variation were as low as 13 ± 3 µm in the lateral plane along the x- and y-axes and −6 ± 15 µm with respect to the nominal value of 107 µm. This micro-assembly technology is applicable to the integration of all microsystems including the interconnection of microfluidic devices, the assembly of hybrid microsystems and the parallel assembly of microdevices.