Printed Circuit Boards

Printed circuit boards (PCBs) are a ubiquitous feature of modern electronics, facilitating the rapid development and mass production of complex electronic devices. However, the commercial techniques of PCB fabrication produce various contaminants that severely degrade the stability and repeatability of the PCBs as a platform for electrochemical sensing. The present study demonstrates that these contaminants can be eliminated by using several pre-cleaning techniques. Thus, the paper provides a novel approach for the exploitation of commercial PCBs as reliable sample-in-answer-out diagnostic microsystems.

Historically, the most common PCB is composed of two copper layers over an insulator material such as flame retardant 4 (FR4). Vias are used to connect the layers, and can be either through or blind. Through vias allow electronic circuit board connections between the top and bottom surfaces, while blind vias connect to internal and external layers. Both are characterized by high conductivity.

In order to build a PCB, designers must first import the net connectivity of the component footprints into a computer-aided design (CAD) system. Then, they must position the parts for their best performance while being mindful of the connectivity between them and areas of excessive heat or noise. This requires experience and a deep understanding of the technology.

Electrochemical Sensors and Printed Circuit Boards

The next step is to turn the rubber-band net connections into drawn traces and planes using the CAD software’s features. This is a laborious task, and great care must be taken to ensure that the traces are the correct length for the signals they are conducting. Additionally, the traces must be routed so that they do not cross each other or other components in an undesirable way. This can be a difficult task for beginners, but with practice and the proper tools, CAD users can become very proficient in this art.

Once the components are placed and routed, it is time to test the circuit. Depending on the complexity of the design, this can be done in a laboratory environment or using a simulation tool. In either case, the results must be compared to the specifications set by the designers. The simulated results must also be taken into account when modeling the operation of the board in a real-world environment.

Some of the most commonly used components on a PCB include capacitors, resistors and sensors. Capacitors store electrical charge and release it when needed in the circuit. Resistors limit the flow of electric current and are usually color-coded with stripes or have their resistance value in ohms printed on them. Sensors detect input from the physical environment such as vibration, motion and acceleration and respond by generating a signal.

Oftentimes, it is necessary to use a reference electrode when performing electrochemical analyses. For example, cyclic voltammetry uses a silver chloride electrode to maintain a constant potential with minimal current passing through it. This reference electrode can be incorporated on a PCB by applying an electroless silver plating process followed by chlorineation. One such example is a PCB-based methylene blue impedimetric sensor that detects the protein biomarker interleukin-12 (IL-12), which is elevated in patients diagnosed with autoimmune disease multiple sclerosis [24].