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APRIL 2020 I PCB007 MAGAZINE 73 LoPCB manufacturing technology by the same PCB manufacturers. A standard microfluidic network (Figure 12a) comprising two inlets and two outlets was designed and fabricated (Figure 12b, c, & e), where the resulting dilu- tion ratio is thermally regulated using a power MOSFET as a heating element (Figure 12c) [6] . The manufacturing process has been devel- oped to produce a three-layer printed circuit utilizing FR-4 laminate. The stackup utilizes a top, middle, and bottom layer. The top layer is silver plated, with the vias as pseudo reference electrodes, if pre-chlorinated. The middle layer is gold plated; thus, vias can be used as sens- ing electrodes since enzymes, antibodies, cells, and microorganisms can be immobilized onto the gold electrode surface, making them effec- tive biosensors. The bottom layer serves as the microfluidic network, interconnecting the inlet and outlet vias of the PCB. The microchannels are formed in dry photoresist (Figure 13). Conclusion As this technology evolves, more materi- als are introduced to see if the overall cost of these devices could be brought down. As seen in Table 1, paper was introduced as well as ceramics, polymers, and then PCBs. Today, 3D printing, printed electronics (PE), and various Figure 12: The PCB-based active control diluter; (a) the diluter design with the heating element and the thermal insulation air gap; (b) the PCB prototype— the top layer comprising inlet and outlet vias; (c) the bottom layer with functional electronics; (d) a microfluidic layout representation for the device; (e) the bottom layer of the microfluidic layer [6] . Figure 13: The PCB-based active control diluter stackup of the developed LoPCB; (a) exploded view; (b) cross-sectional view along the microfluidic channel [6] .