Direct-referencing two-dimensional-array digital microfluidics using multilayer printed circuit board

Digital (i.e., droplet-based) microfluidics, by the electrowetting-on-ditelectric (EWOD) mechanism, has shown great potential for a wide range of applications, such as lab-on-a-chip. While most reported EWOD chips use a series of electrode pads essentially in 1-D line pattern designed for specific tasks, the desired universal chips allowing user-reconfigurable paths would require the electrode pads in 2-D pattern. However, to electrically access the electrode pads independently, conductive lines need to be fabricated underneath the pads in multiple layers, raising a cost issue particularly for disposable chip applications. In this paper, we report the building of digital microfluidic plates based on a printed circuit board (PCB), in which multilayer electrical access lines were created inexpensively using the mature PCB technology. However, due to its surface topography and roughness and resulting high resistance against droplet movement, the as-fabricated PCB surfaces require high (similar to 500 V) voltages unless coated with or immersed in oil. Our goal is the EWOD operations of droplets not only on oil-covered surfaces but also on dry ones. To meet the varying levels of performances, three types of gradually complex post-PCB microfabrication process are developed and evaluated. By introducing land-grid-array sockets in the packaging, a scalable digital microfluidic system with a reconfigurable and low-cost chip is also demonstrated.