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- Design and Optimization of Printed Circuit Boards Reinforced with Natural Fibers Using Computational Finite Element MethodsPublication . Pereira, João Carlos Velosa; Curto, Joana Maria Rodrigues; Mitchell, Geoffrey Robert; Silva, Abílio Manuel Pereira daThe growing environmental concerns and the search for more sustainable solutions have driven research into the development of eco-friendly materials for technological applications. In this context, this thesis addresses the design and optimization of printed circuit boards (PCBs) reinforced with natural fibers, using computational methods based on the Finite Element Method (FEM). The partial or complete replacement of traditional materials with natural fiber composites in PCBs aims to reduce environmental impact without compromising the mechanical, thermal, and electrical performance required for modern electronic applications. The work begins with a critical review of the literature, identifying the main natural fiber (such as eucalyptus, pine, hemp, and bamboo, among others) and their relevant properties for PCB applications. A systematic material selection methodology is then proposed, combining criteria of sustainability, technical performance, and processing feasibility. Computational modelling and simulation are fundamental in this study. Detailed three-dimensional models of composite PCBs were developed, incorporating the typical microstructure of natural fiber composites. The Finite Element Method was employed to analyse the structural behaviour (bending, tensile strength, fatigue) and thermal performance (heat dissipation, thermal expansion) of the new PCBs. Advanced modelling techniques, such as multiscale analysis and property homogenization, were applied to adequately represent the interaction between the polymeric matrix and the natural fiber. The optimization phase involved the use of evolutionary algorithms and multi-objective optimization methods to find the best balance between weight, mechanical strength, thermal conductivity, and cost. Different reinforcement configurations, fiber orientations, and multilayer architectures were simulated and compared. The results demonstrated that it is possible to achieve performance levels comparable to those of conventional materials in several critical metrics, with the added advantage of significantly reducing the carbon footprint of the final products. This thesis includes two studies dedicated to the modelling of solder paste behaviour during printing and reflow processes. The first study develops a two-dimensional model that describes the flow of solder paste through the stencil, analysing aperture filling, the influence of viscosity, and the effects of squeegee dynamics on the final deposition profile. The simulations qualitatively reproduce the patterns observed experimentally, thereby validating the modelling approach. The second study presents a three-dimensional simulation coupled with a six-degrees-of-freedom (6DoF) model and user-defined functions (UDFs) that describe the transition of the solder paste into its molten state. This approach enabled the analysis of the combined behaviour of the paste and the component during the Pin-in-Paste process, encompassing phenomena such as volumetric shrinkage, rheological evolution, surface-tension-driven effects, and meniscus formation. The results demonstrate that numerical modelling is an effective tool for understanding and optimizing soldering processes, particularly when applied to alternative substrates intended to replace conventional laminates. Finally, the industrial impact of this approach is discussed, along with the observed limitations, and future research directions are proposed, including studies on long-term durability, behaviour in harsh environments, and the integration of additive manufacturing techniques to produce eco-friendly PCBs. This work contributes to innovation in the design of sustainable electronic components, paving the way for a new generation of more environmentally friendly devices.