Development of Screen-Printable Multilayer Printed Circuit Boards with Patterned Resistors on Fabric

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Printed Circuit Boards (PCBs) are generally rigid or with limited flexibility, and therefore difficult to adapt for electronic systems on wearable clothing. This thesis investigates PCBs and passive circuit components that can be printed directly onto fabric using common commercially available screen-printing inks. While not stretchable, such PCBs have high flexibility that are comparable to their substrate (e.g., cotton cloth). This thesis directly expands upon previous work that investigated the viability of using screen-printing techniques to build a circuit, called a screen-printed circuit (SPC). The procedure involves designing the circuit in CorelDRAW, using a laser to cut a mold out of sticky paper, and using this paper to pattern conductive ink. While previous research characterized many of the properties of two common commercially available inks (AG 500A and AG-800), that research did not investigate any screen-printed circuits other than basic electronic traces and their use in assembling surface mount technology (SMT) components into passive filters. Furthermore, only single level PCBs were investigated, and the entire circuit needed to be printed at the same time.In this thesis, new techniques are developed that enable more complex circuits to be built. In particular, a procedure to print different parts of the circuit at different times is successfully developed. Furthermore, a technique to create vias analogous to those used in multilayer PCBs is created to allow the development of multilayer SPCs. This research thus enables the development of far more complex SPC designs and components. In addition, purely screenprinted resistors with practical resistor values are created that can be used in many SPCs. A technique is also described to tune a given printed resistor in a predictable way, allowing the creation of SPC resistors with a higher degree of precision. A screen-printed capacitor is also created, and theoretical ways to increase its capacitance investigated; still, the capacitance values of SPC capacitors remain low (picofarads) due to the minimum achievable line separation between capacitor plates achievable with the current printing process.Other limitations of the processes are also investigated. The screen-printing technique has relatively high variance in the traces created this way, and it is difficult to create a component with a specific resistance, although a procedure to create a resistor more precisely is discussed. Furthermore, the complexity of SPC design and manufacturing is greatly increased when sequential printing and multilayer design is required, so future work is encouraged to investigate ways of simplifying this process. Finally, the multilayer procedure has many possibilities that can be further explored, such as changing materials in layers, adding more layers, or investigating how a multiple layer circuit behaves under stretching.
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